Method of assuming acting point of floor reaction force to biped walking mobile body and method of assuming joint moment of biped walking mobile body

ABSTRACT

While a biped walking mobile body is in a motion, such as level-ground walking, the position of the center of gravity (G0) of the biped walking mobile body, the position of an ankle joint ( 12 ) of each leg ( 2 ), and the position of a metatarsophalangeal joint ( 13   a ) of a foot ( 13 ) are successively grasped. The horizontal position of any one of the center of gravity (G0), the ankle joint ( 12 ), and the metatarsophalangeal joint ( 13   a ) is estimated as the horizontal position of a floor reaction force acting point on the basis of the combination of the contact or no contact with the ground at a spot directly below the metatarsophalangeal joint  13   a  of the foot  13  and a spot directly below the ankle joint  12 , which is detected by ground contact sensors  51   f  and  51   r , respectively, provided on the sole of the foot  13 . The vertical position of the floor reaction force acting point is estimated on the basis of the vertical distance from the ankle joint ( 12 ) to a ground contact surface.

TECHNICAL FIELD

The present invention relates to a method of estimating the position ofa floor reaction force acting point of each leg of a biped walkingmobile body, such as a human being or a biped walking robot. The presentinvention further relates to a method of estimating the moment acting ona joint of a leg of the biped walking mobile body by using the estimatedvalue of the position of the floor reaction force acting point.

BACKGROUND ART

To control an operation of, for example, a walking aid apparatus forassisting a human being in walking or to control a traveling motion of abiped walking robot, it is necessary to successively grasp the floorreaction forces acting on legs of the human being or the biped walkingrobot (to be more specific, the forces from a floor that act on groundcontact portions of the legs) and the positions of floor reaction forceacting points. Grasping the floor reaction forces and the floor reactionforce acting points makes it possible to grasp moments or the likeacting on joints of the legs of the biped walking mobile body, and todecide desired auxiliary forces of the walking aid apparatus or desireddrive torques or the like of joints of the biped walking robot on thebasis of the grasped moments or the like.

As a technique for grasping the floor reaction forces, one disclosed in,for example, Japanese Unexamined Patent Application Publication No.2000-249570, has been known. According to this technique, a floorreaction force of each leg is grasped as a resultant value (linearcombination) of a plurality of trigonometric functions having mutuallydifferent cycles of 1/n (n=1, 2, . . . ) of a walking cycle, because thetime-dependent change waveform of a floor reaction force of each legperiodically changes during steady walking of a biped walking body.According to this technique, however, the positions of floor reactionforce acting points cannot be grasped, making the technique inadequatefor grasping moments acting on the joints of legs of the biped walkingmobile body.

There has been also known a technique in which a biped walking mobilebody is walked on a force plate installed on a floor so as to graspfloor reaction forces and the positions of floor reaction force actingpoints on the basis of the outputs of the force plate (refer to, forexample, Japanese Unexamined Patent Application Publication No.2001-29329). This technique, however, presents a problem in that thefloor reaction forces and the positions of floor reaction force actingpoints can be grasped only in an environment wherein a force plate isinstalled, so that the technique cannot be applied to the walking of abiped walking mobile body in a normal environment.

Accordingly, the present applicant has previously proposed in, forexample, Japanese Patent Application No. 2002-18798 (Japanese UnexaminedPatent Application Publication No. 2003-220584), a technique thatpermits real-time estimation of the positions of floor reaction forceacting points. This technique uses the fact that the inclination angleof a thigh of each leg or the bending angle of a knee joint has arelatively high correlation with the position of a floor reaction forceacting point with respect to the ankle of each leg (the positionalvector of a floor reaction force acting point, using the ankle as thereference). More specifically, according to the technique, thecorrelation data (e.g., data tables or arithmetic expressions) showingthe correlation between the inclination angles of thighs or the bendingangles of knee joints and the positions of floor reaction force actingpoints is created and retained in a memory beforehand, and the positionsof floor reaction force acting points are estimated from the correlationdata and the inclination angles of thighs or the bending angles of kneejoints measured while a biped walking mobile body is walking.

However, further experiment and study by the inventors of the presentapplication have revealed that the correlation between the inclinationangles of thighs or the bending angles of knee joints and the positionsof floor reaction force acting points is influenced by the walking speedor the like of a biped walking mobile body and further influenced by themotion modes of a biped walking mobile body, such as a level-groundwalking mode, a staircase walking mode, and a slope walking mode. Hence,in order to properly estimate the positions of the floor reaction forceacting points by the aforementioned technique, it has been necessary toprepare a plurality of types of the above correlation data for eachwalking speed or motion mode of the biped walking mobile body and toretain them in a memory beforehand, inconveniently taking up a majorpart of the capacity of the memory. There has been another inconveniencein that, when a motion mode is changed over, discontinuity in positionof a floor reaction force acting point estimated on the basis of anothercorrelation data is likely to occur before or after the changeover,resulting in a discontinuously changed estimated value of a joint momentwhen the estimated position of the floor reaction force acting point isused to estimate the joint moment.

The present invention has been made in view of the above background, andit is an object of the present invention to provide a floor reactionforce acting point estimating method that makes it possible to grasp, inreal time, the position of a floor reaction force acting point by arelatively simple technique without using a plurality of types ofcorrelation data, and that is particularly suited for grasping theposition of a floor reaction force acting point related to a human beingas a biped walking mobile body.

Moreover, it is another object of the present invention to provide amethod of estimating a joint moment of the biped walking mobile bodythat makes it possible to grasp, in real time, the moment acting on ajoint, such as a knee joint of a leg, by using the aforesaid estimatedvalue of a floor reaction force acting point.

DISCLOSURE OF INVENTION

The findings obtained by great efforts, including a variety ofexperiments, made by the inventors of the present application, indicatethat, when a biped walking mobile body, such as a human being, iswalking on a level ground, for example, the horizontal position of thefloor reaction force acting point of each leg in contact with the groundis usually substantially equal to one of the positions of the horizontalposition of the center of gravity of the biped walking mobile body, thehorizontal position of the metatarsophalangeal joint of the foot of theleg (the joint of the thumb root of the foot), and the horizontalposition of the ankle joint of the leg, depending on which place of thefoot of the leg is in contact with the ground, independently of themoving speed or the motion mode or the like of the biped walking mobilebody. To be more specific, on each leg, if the leg is in contact withthe ground at the place substantially directly below themetatarsophalangeal joint (a place adjacent to the toe) with the heelside of the foot not in contact with the ground, then the horizontalposition of the floor reaction force acting point related to the legwill be substantially equal to the horizontal position of themetatarsophalangeal joint, or if the leg is in contact with the groundat the place substantially directly below the ankle joint (a placeadjacent to the heel) with the toe side of the foot not in contact withthe ground, then, the horizontal position of the floor reaction forceacting point related to the leg will be substantially equal to thehorizontal position of the ankle joint. Further, if both the placeadjacent to the toe of the foot and the place adjacent to the heel ofthe foot are in contact with the ground (substantially the entire soleof the foot is in contact with the ground), then the horizontal positionof the floor reaction force acting point related to the leg will besubstantially equal to the horizontal position of the center of gravityof the biped walking mobile body in most cases. Thus, the horizontalpositions of the floor reaction force acting points of each leg can beestimated by successively grasping the center of gravity of the bipedwalking mobile body and the positions (especially the horizontalpositions) of the ankle joint and the metatarsophalangeal joint of theleg and also by grasping which place of the foot of the leg in contactwith the ground is in contact with the ground. Moreover, the verticalposition of the floor reaction force acting point of each leg in contactwith the ground, especially the vertical position relative to an anklejoint, is defined by the vertical distance from the ankle joint to theground contact surface of the leg.

Thus, to fulfill the objects described above, according to a method ofestimating a floor reaction force acting point of a biped walking mobilebody in accordance with the present invention, i.e., a method ofsuccessively estimating the position of the floor reaction force actingpoint of each leg of a biped walking mobile body, in the sole of thefoot of each leg of the biped walking mobile body, a first groundcontact sensor and a second ground contact sensor that output groundcontact detection signals based on the contact or no contact of a placedirectly below an ankle joint of a leg and a place directly below ametatarsophalangeal joint of the foot of the leg, respectively, areprovided. The method includes a first step for successively grasping theposition of the center of gravity of the biped walking mobile body, theposition of the ankle joint of each leg, and the position of themetatarsophalangeal joint of the foot of the leg, respectively, and alsosuccessively grasping the vertical distance from the ankle joint to aground contact surface of each leg in contact with the ground while thebiped walking mobile body is in motion, and

a second step for successively estimating selectively the horizontalposition of one of the center of gravity, the ankle joint of the leg,and the metatarsophalangeal joint of the leg, the positions thereofhaving been determined in the first step, as the horizontal position ofthe floor reaction force acting point of the leg on the basis of atleast the combination of contact or no contact indicated by a groundcontact detection signal of the first ground contact sensor and contactor no contact indicated by a ground contact detection signal of thesecond ground contact sensor for each leg in contact with the groundwhile the biped walking mobile body is in motion, and also successivelyestimating the vertical position of the floor reaction force actingpoint of the leg as the position apart vertically downward from theankle joint by the vertical distance from the ankle joint to the groundcontact surface of the leg determined in the first step.

According to the method of estimating a floor reaction force actingpoint in accordance with the present invention, the position of thecenter of gravity of a biped walking mobile body, the position of theankle joint of each leg, and the position of the metatarsophalangealjoint of the foot of the leg are successively grasped respectively, andthe horizontal position of one of the center of gravity, the anklejoint, and the metatarsophalangeal joint is selectively estimatedsuccessively as the horizontal position of the floor reaction forceacting point of the leg on the basis of the combination of contact or nocontact at respective places, which is indicated by ground contactdetection signals of the first and the second ground contact sensorsprovided at two places (the place directly below the ankle joint and theplace directly below the metatarsophalangeal joint) of the sole of thefoot of each leg. This arrangement allows the horizontal position of afloor reaction force acting point to be estimated without using a datatable, or map data or the like. Moreover, the vertical distance from theankle joint to a ground contact surface (floor surface) of each leg incontact with the ground is successively grasped in the first step,thereby estimating the position vertically apart downward from the anklejoint by that vertical distance as the vertical position of the floorreaction force acting point, so that it is possible to estimate thevertical position of a floor reaction force acting point without using adata table, or map data or the like.

Thus, according to the method of estimating a floor reaction forceacting point in accordance with the present invention, the position of afloor reaction force acting point can be grasped in real time by arelatively simple technique without using a plurality of types ofcorrelation data.

The method of estimating a floor reaction force acting point inaccordance with the present invention makes it possible to grasp theposition of the center of gravity, the position of an ankle joint, andthe position of a metatarsophalangeal joint by detecting, for example,the inclination angle of a body by a gyro-sensor or an accelerationsensor and by detecting the bending angle of a joint of each leg by apotentiometer or the like, and then by using the detected inclinationangle of the body, the detected bending angle of the joint of the leg,and a rigid link model representing a biped mobile body in the form of arigid linkage assembly.

According to the method of estimating a floor reaction force actingpoint in accordance with the present invention, basically, if a groundcontact detection signal of the first ground contact sensor of each legis a signal indicating contact with the ground and a ground contactdetection signal of the second ground contact sensor of the leg is asignal indicating no contact with the ground, then the horizontalposition of the ankle joint of the leg may be estimated as thehorizontal position of a floor reaction force acting point of the leg,or if a ground contact detection signal of the first ground contactsensor of each leg is a signal indicating no contact with the ground anda ground contact detection signal of the second ground contact sensor ofthe leg is a signal indicating contact with the ground, then thehorizontal position of the metatarsophalangeal joint of the leg may beestimated as the horizontal position of a floor reaction force actingpoint of the leg, or if ground contact detection signals of both thefirst ground contact sensor and the second ground contact sensor of eachleg are signals indicating contact with the ground, then the horizontalposition of the center of gravity may be estimated as the horizontalposition of a floor reaction force acting point of the leg.

However, depending on the motion mode or the like of a biped walkingmobile body, if ground contact detection signals of both the firstground contact sensor and the second ground contact sensor of each legare signals indicating contact with the ground, i.e., the place directlybelow the ankle joint (the sole on the heel side) and the place directlybelow the metatarsophalangeal joint (the sole on the toe side) are incontact with the ground (including contact that hardly produces a load),then a situation may occur in which the position of the center ofgravity of the biped walking mobile body is behind the position of theankle joint of the leg in contact with the ground or before the positionof the metatarsophalangeal joint in the advancing direction of the bipedwalking mobile body. In such a case, the horizontal position of thecenter of gravity deviates from the ground contact surface of the leg.Hence, if the horizontal position of the center of gravity is estimatedas the horizontal position of a floor reaction force acting point, thenthe estimating position will be inaccurate with respect to thehorizontal position of a normal floor reaction force acting point thatshould exist within a ground contact surface of the leg. Further, if thecenter of gravity of the biped walking mobile body exists behind theposition of the ankle joint of the leg in contact with the ground, thenthe floor reaction force related to the leg is generally concentrated ona place adjacent to the heel of the foot of the leg (that is, a place inthe vicinity of the first ground contact sensor). Further, if the centerof gravity of the biped walking mobile body exists before the positionof the metatarsophalangeal joint of the foot of the leg in contact withthe ground, then the floor reaction force related to the leg isgenerally concentrated on a place adjacent to the toe of the leg (thatis, a place in the vicinity of the second ground contact sensor).

Therefore, according to the method of estimating a floor reaction forceacting point in accordance with the present invention, to estimate thehorizontal position of the floor reaction force acting point in thesecond step, on each leg in contact with the ground, preferably, if aground contact detection signal of the first ground contact sensor ofeach leg is a signal indicating contact with the ground and if a groundcontact detection signal of the second ground contact sensor of the legis a signal indicating no contact with the ground, then the horizontalposition of the ankle joint of the leg is estimated as the horizontalposition of a floor reaction force acting point of the leg, or if aground contact detection signal of the first ground contact sensor ofeach leg is a signal indicating no contact with the ground and if aground contact detection signal of the second ground contact sensor ofthe leg is a signal indicating contact with the ground, then thehorizontal position of the metatarsophalangeal joint of the leg isestimated as the horizontal position of a floor reaction force actingpoint of the leg, or if ground contact detection signals of both thefirst ground contact sensor and the second ground contact sensor of eachleg are signals indicating contact with the ground and if the positionof the center of gravity is behind the position of the ankle joint ofthe leg in the advancing direction of the biped walking mobile body,then the horizontal position of the ankle joint of the leg is estimatedas the horizontal position of a floor reaction force acting point of theleg, or if ground contact detection signals of both the first groundcontact sensor and the second ground contact sensor of each leg aresignals indicating contact with the ground and if the position of thecenter of gravity is before the position of the metatarsophalangealjoint of the leg in the advancing direction of the biped walking mobilebody, then the horizontal position of the metatarsophalangeal joint ofthe leg is estimated as the horizontal position of a floor reactionforce acting point of the leg, or if ground contact detection signals ofboth the first ground contact sensor and the second ground contactsensor of each leg are signals indicating contact with the ground and ifthe position of the center of gravity is between the position of theankle joint of the leg and the position of the metatarsophalangeal jointin the advancing direction of the biped walking mobile body, then thehorizontal position of the center of gravity is estimated as thehorizontal position of a floor reaction force acting point of the leg.

With this arrangement, the accuracy of estimating the horizontalposition of a floor reaction force acting point can be enhancedindependently of the motion mode or the like of the biped walking mobilebody.

Further, according to the method of estimating a floor reaction forceacting point in accordance with the present invention, regarding theestimation of the vertical position of a floor reaction force actingpoint, the vertical distance from the ankle joint to a ground contactsurface of each leg when the biped walking mobile body is in, forexample, an upright stationary state, is measured and retained in amemory beforehand, and when the vertical distance from the ankle jointto the ground contact surface of each leg in contact with the ground isgrasped in the first step, the vertical distance retained in the memoryis grasped as the vertical distance from the ankle joint to the groundcontact surface of each leg in contact with the ground. The uprightstationary state of the biped walking mobile body more technically meansa state wherein the biped walking mobile body is standing with both legsthereof and its body stretched substantially in the vertical directionand with substantially entire surfaces of the soles of the feet of bothlegs in contact with the ground.

More specifically, according to the knowledge of the inventors of thepresent application, the vertical distance from the ankle joint to theground contact surface of the leg in contact with the ground generallydoes not change much while the biped walking mobile body is in a motion,such as walking on a level ground, and will be approximately almostequal to the vertical distance from the ankle joint to the groundcontact surface of each leg while the biped walking mobile body is inthe upright stationary state. Hence, the vertical position of a floorreaction force acting point can be easily estimated by measuring andretaining in a memory beforehand the vertical distance from the anklejoint to the ground contact surface of each leg in the uprightstationary state, and by grasping the vertical distance retained in thememory as the vertical distance from the ankle joint to the groundcontact surface of the leg in contact with the ground while the bipedwalking mobile body is in motion.

To estimate the vertical position of a floor reaction force acting pointwith even higher accuracy, preferably, the vertical distance from theankle joint to the ground contact surface of each leg and the verticaldistance from the metatarsophalangeal joint to the ground contactsurface of the leg while the biped walking mobile body is in the uprightstationary state are measured and retained in a memory beforehand as afirst basic vertical distance and a second basic vertical distance,respectively, and when the vertical distance from the ankle joint to theground contact surface of each leg in contact with the ground is graspedin the first step, if the position of the center of gravity is behindthe position of the metatarsophalangeal joint of the leg in theadvancing direction of the biped walking mobile body, then the firstbasic vertical distance is grasped as the vertical distance from theankle joint to the ground contact surface of the leg, or if the positionof the center of gravity is before the position of themetatarsophalangeal joint in the advancing direction of the bipedwalking mobile body, then the vertical distance between the ankle jointand the metatarsophalangeal joint of the leg is determined and then thevalue obtained by adding the second basic vertical distance to thedetermined vertical distance is grasped as the vertical distance fromthe ankle joint to the ground contact surface of the leg.

More specifically, if the position of the center of gravity is behindthe position of the metatarsophalangeal joint of a leg in the advancingdirection of the biped walking mobile body, then at least bottom surfaceof the heel of the foot of the leg is in contact with the ground, sothat the vertical distance from the ankle joint to the ground contactsurface of the leg in contact with the ground while the biped walkingmobile body is in motion is substantially equal to the first basicvertical distance. Further, if the position of the center of gravity isbefore the position of the metatarsophalangeal joint of the leg in theadvancing direction of the biped walking mobile body, then the foot ofthe leg is normally in contact with the ground at a place adjacent toits toe (a place near the metatarsophalangeal joint), whereas its heelis floating. In this case, the vertical distance from a foot joint ofthe leg to the ground contact surface is substantially equal to thevalue obtained by adding the second basic vertical distance to thevertical distance between the foot joint and the metatarsophalangealjoint. In this case, the vertical distance between the foot joint andthe metatarsophalangeal joint can be determined from the positions ofthose joints grasped in the first step.

Thus, by grasping the vertical distance from the ankle joint to theground contact surface of a leg according as whether the position of thecenter of gravity is behind or before the position of themetatarsophalangeal joint in the advancing direction of the bipedwalking mobile body, as described above, the accuracy of the verticaldistance can be enhanced. As a result, the accuracy of an estimatedvalue of the vertical position of a floor reaction force acting pointcan be further enhanced.

Next, a method of estimating a joint moment of a biped walking mobilebody in accordance with the present invention is a method of estimatinga moment acting on at least one joint of each leg of a biped walkingmobile body by using an estimated value of the position of a floorreaction force acting point successively determined by the floorreaction force acting point estimating method according to the presentinvention described above. And this joint moment estimating methodincludes a step for successively estimating the floor reaction force ofeach leg, which is in contact with the ground, of the biped walkingmobile body by using at least a detection output of an accelerationsensor attached to a body of the biped walking mobile body to detect theacceleration of a predetermined part of the body of the biped walkingmobile body and a detection output of a body inclination sensor attachedto the body to detect an inclination angle of the body, and a step forsuccessively grasping the inclination angle of each rigid correspondingpart of a biped walking mobile body that corresponds to each rigid bodyof a rigid link model representing the biped walking mobile body in theform of a link assembly of a plurality of rigid bodies, the accelerationof the center of gravity of the rigid corresponding part, and theangular acceleration of the rigid corresponding part by using at leastdetection outputs of the body inclination sensor and an angle sensorattached to a joint to detect the bending angle of a joint of each legof the biped walking mobile body, wherein the moment acting on at leastone joint of each leg of the biped walking mobile body is estimated onthe basis of an inverse dynamics model by using an estimated value ofthe floor reaction force, an estimated value of the position of thefloor reaction force acting point, an inclination angle of the aforesaideach rigid corresponding part, an acceleration of the center of gravityof the rigid corresponding part and an angular acceleration of the rigidcorresponding part, the weight and size of each rigid corresponding partdetermined in advance, the position of the center of gravity of eachrigid corresponding part in the rigid corresponding part determined inadvance, and an inertial moment of each rigid corresponding partdetermined in advance.

According to the joint moment estimating method in accordance with thepresent invention, although it will be discussed in detail later,successively detecting the acceleration of a predetermined part (e.g.,the waist) of a body (torso) of a biped walking mobile body by anacceleration sensor and also successively detecting the inclinationangle of the body by a body inclination sensor allow the floor reactionforce acting on each leg in contact with the ground to be successivelyestimated by using the detection outputs (detected values). Further,successively detecting the bending angle of a joint of each leg by anangle sensor in addition to detecting the inclination angle of the bodyby a body inclination sensor makes it possible to successively grasp theinclination angle (this indicates the mutual posture relationship amongrigid corresponding parts) of each rigid corresponding part (thigh,crus, etc.) of a rigid link model representing a biped walking mobilebody, the acceleration of the center of gravity of the rigidcorresponding part, and the angular acceleration of the rigidcorresponding part by using the detection outputs (detected values) ofthe aforesaid body inclination sensor and the angle sensor. This meansthat the mutual posture relationship among rigid corresponding partswill be known if the inclination angle of the body and the bendingangles of joints of each leg are known, so that the inclination anglesof the rigid corresponding parts will be known. Further, the position ofthe center of gravity of a rigid corresponding part in the rigidcorresponding part (the position of the center of gravity of the rigidcorresponding part in a coordinate system fixed to each rigidcorresponding part) can be determined in advance; therefore, based onthis and the mutual posture relationship among the rigid correspondingparts, the position of the center of gravity of each rigid correspondingpart (the position relative to a reference point fixed at an arbitraryposition (e.g., the waist) of a biped walking mobile body) in the entirebiped walking mobile body (in the entire rigid link model) can be known.And, the acceleration of the center of gravity can be grasped as thesecond-order differentiation value of the position of the center ofgravity of each rigid corresponding part. Further, if the inclinationangle of each rigid corresponding part is known, then the angularacceleration of each rigid corresponding part can be grasped as thesecond-order differentiation value thereof.

Further, when the floor reaction force of a biped walking mobile bodyhas been estimated, and the inclination angle of each rigidcorresponding part, the acceleration of the center of gravity of therigid corresponding part, and the angular acceleration of the rigidcorresponding part have been grasped, as described above, these piecesof data and the estimated value of a floor reaction force acting pointdetermined by the aforesaid floor reaction force acting point estimatingmethod, the weight and size (especially length) of each rigidcorresponding part determined in advance, the position of the center ofgravity of each rigid corresponding part in the rigid corresponding partdetermined in advance, and the inertial moment of each rigidcorresponding part determined in advance can be used to estimate themoment acting on a knee joint or a hip joint of each leg on the basis ofa publicly known so-called inverse dynamics model. Briefly speaking, thetechnique based on the inverse dynamics model uses an equation of motionrelated to the translational motion of the center of gravity of eachrigid corresponding part of a biped walking mobile body and an equationof motion related to a rotational motion of the rigid corresponding part(e.g., the rotational motion about the center of gravity of the rigidcorresponding part) to determine the moments acting on joints of thebiped walking mobile body that correspond to the joints of a rigid linkmodel in order from the one closest to a floor reaction force actingpoint. Although it will be discussed in detail later, if it is assumedthat, for example, each leg is a link assembly having a thigh and a crusas rigid corresponding parts, then the force acting on the knee joint ofthe leg (the joint reaction force) will be known by applying theacceleration of the center of gravity of the crus, an estimated value ofthe floor reaction force acting on the leg, and a value of the weight ofthe crus to the equation of motion related to the translational motionof the center of gravity of the crus of each leg. Furthermore, themoment of the knee joint of the leg can be estimated by applying a jointreaction force acting on the knee joint of the leg, an angularacceleration of the crus of the leg, an estimated position of the floorreaction force acting point of the leg, an estimated value of the floorreaction force of the leg, the position of the center of gravity of thecrus in the crus, a data value related to the size (length) of the crus,a value of the inertial moment of the crus, and a value of theinclination angle of the crus to an equation of motion related to arotational motion of the crus.

In addition, the joint reaction force acting on the hip joint of the legcan be determined by applying an acceleration of the center of gravityof the thigh, a joint reaction force acting on the knee joint of theleg, and a value of the weight of the thigh to an equation of motionrelated to the translational motion of the center of gravity of thethigh of each leg. Further, the moment of the hip joint of the leg canbe estimated by applying joint reaction forces acting on the knee jointand the hip joint, respectively, of the leg, an angular acceleration ofthe thigh of the leg, a position of the center of gravity of the thighin the thigh and a data value related to the size (length) of the thigh,a value of the inertial moment of the thigh, and a value of theinclination angle of the thigh to an equation of motion related to therotational motion of the thigh.

The joint moment estimating method in accordance with the presentinvention makes it possible to estimate, in real time, the moment actingon a joint of a leg by relatively simple arithmetic processing by usingan estimated value of the position of a floor reaction force actingpoint estimated according to the floor reaction force acting pointestimating method in accordance with the present invention describedabove so as to estimate the moment acting on a joint of a leg, thusobviating the need for preparing multiple types of correlation databeforehand or for attaching a relatively large sensor or the like to abiped walking mobile body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 (a) and (b) are diagrams for explaining a basic principle of amethod of estimating floor reaction forces in an embodiment of thepresent invention,

FIG. 2 is a diagram schematically showing a human being as a bipedalwalking mobile body and a construction of an apparatus installed on thehuman being in an embodiment of the present invention,

FIG. 3 is a block diagram for explaining the functions of an arithmeticprocessing unit installed in the apparatus shown in FIG. 2, and

FIG. 4 is a diagram showing a rigid link model used for processing ofthe arithmetic processing unit shown in FIG. 3.

FIG. 5 is a diagram for explaining a technique for calculating theposition (horizontal position) of a metatarsophalangeal joint in a firstembodiment of the present invention and a technique for grasping thedistance from an ankle joint to a ground contact surface,

FIGS. 6 (a) and (b) and FIGS. 7 (a) to (c) are diagrams for explaining atechnique for estimating the horizontal positions of floor reactionforce acting points, and

FIG. 8 is a diagram for explaining the processing in a joint momentestimating means of the arithmetic processing unit of FIG. 3.

FIG. 9 and FIG. 10 are graphs illustrating the time-dependent changes inthe horizontal position and the vertical position, respectively, of afloor reaction force acting point in a level-ground walking modedetermined according to the first embodiment of the present invention,

FIG. 11 and FIG. 12 are graphs illustrating the time-dependent changesin a knee joint moment and a hip joint moment, respectively, in thelevel-ground walking mode determined according to the first embodimentof the present invention,

FIG. 13 and FIG. 14 are graphs illustrating the time-dependent changesin a knee joint moment and a hip joint moment, respectively, in astaircase descent walking mode determined according to the firstembodiment of the present invention,

FIG. 15 and FIG. 16 are graphs illustrating the time-dependent changesin a knee joint moment and a hip joint moment, respectively, in astaircase ascent walking mode determined according to the firstembodiment of the present invention,

FIG. 17 and FIG. 18 are graphs illustrating the time-dependent changesin a knee joint moment and a hip joint moment, respectively, in asitting-onto-a-chair mode determined according to the first embodimentof the present invention, and

FIG. 19 and FIG. 20 are graphs illustrating the time-dependent changesin a knee joint moment and a hip joint moment, respectively, in arising-from-a-chair mode determined according to the first embodiment ofthe present invention.

FIG. 21 is a diagram for explaining a technique for calculating theposition of a metatarsophalangeal joint in a second embodiment of thepresent invention and a technique for grasping the distance from anankle joint to a ground contact surface.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment to which a method of estimating a floor reaction forceacting point and a method of estimating a joint moment in accordancewith the present invention will be explained with reference to theaccompanying drawings. First, for the convenience of understanding, thebasic concept of the technique for estimating floor reaction forces of abiped walking mobile body in the embodiment of the present inventionwill be explained with reference to FIG. 1. The motional state of a legof a biped walking mobile body, e.g., the motional state of a leg in awalking mode, comes in a single stance state in which only one leg 2(the front leg, as observed in the advancing direction of a bipedwalking mobile body 1 in the figure) of both legs 2 and 2 of the bipedwalking mobile body 1 is in contact with the ground, as shown in FIG. 1(a), and a double stance state in which both legs 2 and 2 are in contactwith the ground, as shown in FIG. 1( b).

Here, first, in the single stance state, the equation of motion (to bemore specific, an equation of motion related to the translational motionof a center of gravity) of the center of gravity of the biped walkingmobile body 1 in an absolute coordinate system fixed to the floor onwhich the biped walking mobile body 1 moves provides a relationalexpression in which the product of the acceleration of the center ofgravity and the weight of the biped walking mobile body 1 is equal tothe resultant force of the gravity acting on the center of gravity(=weight of the biped walking mobile body 1×acceleration of gravity) andthe floor reaction force acting from the floor to the ground contactportion of the leg 2 in contact with the ground. Specifically, as shownin, for example, FIG. 1 (a), if the components of an acceleration a(vector) of a center of gravity G0 of the biped walking mobile body 1 inan X-axis direction (the horizontal direction relative to the advancingdirection of the biped walking mobile body 1) and in a Z-axis direction(the vertical direction) are denoted by ax and az, respectively, and thecomponents of a floor reaction force F (vector) related to the leg 2 incontact with the ground (the supporting leg 2) in the X-axis directionand the Z-axis direction are denoted by Fx and Fz, respectively, in anabsolute coordinate system Cf fixed to a floor A, then the equation ofmotion of the center of gravity G0 is represented by Equation (1) givenbelow.^(T)(Fx,Fz−M·g)=M· ^(T)(ax,az)  (1)

(where M: Weight of the biped walking mobile body, g: Acceleration ofgravity)

The parenthesized portions ^(T)( , ) on both sides in Equation (1) meanthe vectors of two components. In the present description, the notationof ^(T)( , ) will denote a vector.

Thus, if the acceleration a=^(T)(ax, az) of the center of gravity GG0 ofthe biped walking mobile body 1 is grasped, then the estimated value ofthe floor reaction force F=^(T)(Fx, Fz) can be obtained according to thefollowing Equation (2) by using the acceleration a, the value of theweight M of the biped walking mobile body 1, and the value of theacceleration of gravity g.^(T)(Fx,Fz)=M· ^(T)(ax,az−g)  (2)

In this case, the weight M necessary to obtain the estimated value ofthe floor reaction force F can be grasped beforehand by measurement orthe like. Although it will be discussed in detail hereinafter, theposition and the acceleration a of the center of gravity G0 can besuccessively grasped by a publicly known technique or the like by usingoutputs of sensors, such as a sensor for detecting bending angles(rotational angles) of joints of the biped walking mobile body 1, anacceleration sensor, and a gyro sensor.

An equation of motion of the center of gravity of the biped walkingmobile body 1 (specifically, an equation of motion related to thetranslational motion of the center of gravity) in the state wherein bothlegs are in contact with the ground provides a relational expression inwhich the product of the acceleration of the center of gravity and theweight of the biped walking mobile body 1 is equal to the resultantforce of the gravity acting on the center of gravity (=weight of thebiped walking mobile body×acceleration of gravity) and the floorreaction forces acting from the floor to the ground contact portion ofeach of the two legs 2 and 2 (two floor reaction forces associated withthe two legs 2 and 2, respectively). Specifically, as shown in, forexample, FIG. 1 (b), if the XZ coordinate components of a floor reactionforce Ff related to the leg 2 at the front side with respect to theadvancing direction of the biped walking mobile body 1 are denoted byFfx and Ffz, and the XZ coordinate components of a floor reaction forceFr related to the leg 2 at the rear side are denoted by Frx and Frz,then the equation of motion of the center of gravity G0 is representedby Equation (3) given below.^(T)(Ffx+Frx,Ffz+Frz−M·g)=M· ^(T)(ax,az)  (3)

The meanings of ax, az, M, and g in Equation (3) are as described above.

Meanwhile, according to the knowledge of the inventors of the presentapplication, the floor reaction forces Ff and Fr related to the legs 2and 2, respectively, in the double stance state may be considered togenerally act toward the center of gravity G0 of the biped walkingmobile body 1 from particular parts in the vicinity of the bottom endsof the legs 2 and 2, e.g., the portions of ankle joints 12 f and 12 r,as shown in FIG. 1 (b). And, at this time, a certain relationalexpression holds between the positions of the ankle joints 12 f and 12 rof the legs 2 and 2 relative to the center of gravity G0 and the floorreaction forces Ff and Fr acting on the legs 2 and 2, that is, arelational expression representing a relationship in which the directionof a segment connecting the center of gravity G0 and the ankle joints 12f and 12 r of the legs 2 and 2 (the direction of the positional vectorsof the ankle joints 12 f and 12 r relative to the center of gravity G0 )agrees with the direction of the floor reaction forces Ff and Fr relatedto the legs 2 and 2.

Specifically, referring to FIG. 1 (b), if the coordinates of theposition of the center of gravity G0 in the absolute coordinate systemCf is denoted by (Xg, Zg), the coordinates of the position of the anklejoint 12 f of the leg 2 at the front side is denoted by (Xf, Zf), andthe coordinates of the position of the ankle joint 12 r of the leg 2 atthe rear side is denoted by (Xr, Zr), then the above relationalexpression will be the following equation (4):(Zf−Zg)/(Xf−Xg)=Ffz/Ffx(Zr−Zg)/(Xr−Xg)=Frz/Frx  (4)

Equation (5) given below is derived from the Equation (4) and the aboveEquation (3):

$\begin{matrix}{\begin{matrix}{{Ffx} = {M \cdot \{ {\Delta\;{{Xf} \cdot ( {{\Delta\;{{Zr} \cdot {ax}}} - {\Delta\;{{Xr} \cdot {az}}} -} }} }} \\{  {\Delta\;{{Xr} \cdot g}} ) \}/( {{\Delta\;{{Xf} \cdot \Delta}\;{Zr}} - {\Delta\;{{Xr} \cdot \Delta}\;{Zf}}} )}\end{matrix}\begin{matrix}{{Ffz} = {M \cdot \{ {\Delta\;{{Zf} \cdot ( {{\Delta\;{{Zr} \cdot {ax}}} - {\Delta\;{{Xr} \cdot {az}}} -} }} }} \\{  {\Delta\;{{Xr} \cdot g}} ) \}/( {{\Delta\;{{Xf} \cdot \Delta}\;{Zr}} - {\Delta\;{{Xr} \cdot \Delta}\;{Zf}}} )}\end{matrix}\begin{matrix}{{Frx} = {M \cdot \{ {\Delta\;{{Xr} \cdot ( {{{- \Delta}\;{{Zf} \cdot {ax}}} + {\Delta\;{{Xf} \cdot {az}}} +} }} }} \\{  {\Delta\;{{Xf} \cdot g}} ) \}/( {{\Delta\;{{Xf} \cdot \Delta}\;{Zr}} - {\Delta\;{{Xr} \cdot \Delta}\;{Zf}}} )}\end{matrix}\begin{matrix}{{Frz} = {M \cdot \{ {\Delta\;{{Zr} \cdot ( {{{- \Delta}\;{{Zf} \cdot {ax}}} + {\Delta\;{{Xf} \cdot {az}}} +} }} }} \\{ \Delta\;{{Xf} \cdot g} ){\}/( {{\Delta\;{{Xf} \cdot \Delta}\;{Zr}} - {\Delta\;{{Xr} \cdot \Delta}\;{Zf}}} )}}\end{matrix}\begin{matrix}( {{{{where}{~~~}\Delta\;{Xf}} = {{Xf} - {Xg}}},}  \\{{{\Delta\;{Zf}} = {{Zf} - {Zg}}},} \\{{{\Delta\;{Xr}} = {{Xr} - {Xg}}},} \\ {{\Delta\;{Zr}} = {{Zr} - {Zg}}} )\end{matrix}} & (5)\end{matrix}$

Accordingly, if the acceleration a=^(T)(ax, az) of the center of gravityG0 of the biped walking mobile body 1 is grasped and the positions ofthe ankle joints 12 f, 12 r of the legs 2, 2 relative to the center ofgravity G0 of the biped walking mobile body 1 (these are denoted by ΔXf,ΔZf, ΔXr, and ΔZr in Equation (5)) are grasped, then the estimatedvalues of the floor reaction forces Ff=^(T)(Ffx, Ffz) and Fr=^(T)(Frx,Frz) of each leg 2 can be obtained according to the above Equation (5)by using the acceleration a, the positions of the ankle joints 12 f, 12r, the value of the weight M of the biped walking mobile body 1, and thevalue of the acceleration of gravity g.

In this case, the weight M necessary to obtain the estimated values ofthe floor reaction forces Ff and Fr can be grasped beforehand bymeasurement or the like. Although it will be discussed in detailhereinafter, the acceleration a of the center of gravity G0, theposition of the center of gravity G0, and the positions of the anklejoints 12 f, 12 r relative to the center of gravity G0can besuccessively grasped by a publicly known technique or the like by usingoutputs of sensors, such as a sensor for detecting bending angles(rotational angles) of joints of the biped walking mobile body 1, anacceleration sensor, and a gyro sensor.

The embodiments (first and second embodiments) explained below areadapted to estimate the floor reaction force acting point and jointmoments of each leg 2 while estimating the floor reaction force of eachleg 2 at the same time on the basis of the matters explained above.

The first embodiment in which the present invention has been applied toa human being as a biped walking mobile body will now be explained indetail.

As schematically shown in FIG. 2, a human being 1 is roughly constructedof a pair of right and left legs 2, 2, a torso 5 composed of a waist 3and a chest 4, a head 6, and a pair of right and left arms 7, 7. In thetorso 5, the waist 3 is connected to the legs 2, 2 through theintermediary of a pair of right and left hip joints 8, 8, and issupported on the two legs 2, 2. The chest 4 of the torso 5 exists on theupper side of the waist 3 such that it can be tilted toward the front ofthe human being 1 with respect to the waist 3. And, the arms 7, 7 areprovided such that they extend from right and left sides of the upperpart of the chest 4, and the head 6 is supported on the upper end of thechest 4.

Each of the legs 2 and 2 has a thigh 9 extending from the hip joint 8and a crus 11 extending from the distal end of the thigh 9 through theintermediary of a knee joint 10, a foot 13 being connected to the distalend of the crus 11 through the intermediary of an ankle joint 12.

In the present embodiment, an apparatus described below is attached tothe human being 1 to estimate a floor reaction force acting on each leg2 of the human being 1 that has such a construction, and the actingpoint thereof, and also to estimate the moments acting on the kneejoints 10 and the hip joints 8.

More specifically, attached to the chest 4 of the torso 5 are a gyrosensor 14 that generates outputs based on angular velocities involved ininclinations of the chest 4 (hereinafter referred to as “the chest gyrosensor 14”), an acceleration sensor 15 that generates outputs based onlongitudinal accelerations of the chest 4 (hereinafter referred to as“the chest longitudinal acceleration sensor 15”), an arithmeticprocessing unit 16 constructed of a CPU, a RAM, a ROM, etc., and abattery 17 that provides a power supply of the arithmetic processingunit 16, etc. In this case, these chest gyro sensor 14, the chestlongitudinal acceleration sensor 15, the arithmetic processing unit 16,and the battery 17 are accommodated in a shoulder-bag type housingmember 18 secured to, for example, the chest 4, through a belt or thelike, which is not shown, and are integrally secured to the chest 4through the intermediary of the housing member 18.

More technically, the acceleration indicated by an output of the chestlongitudinal acceleration sensor 15 is the longitudinal acceleration inthe direction of a horizontal section of the chest 4 (the directionorthogonal to the axis of the chest 4), and it is the acceleration inthe longitudinal horizontal direction (in the direction of the X-axis ofthe absolute coordinate system Cf of FIG. 2) in a state wherein thehuman being 1 is standing upright on a level ground, while in a statewherein the waist 3 or the chest 4 is inclined from the verticaldirection (the direction of the Z-axis of the absolute coordinate systemCf of FIG. 2), it is the acceleration in the direction inclined relativeto the horizontal direction by an inclination angle relative to thevertical direction of the chest 4.

Further, a gyro sensor 19 that generates outputs based on angularvelocities involved in inclinations of the waist 3 (hereinafter referredto as “the waist gyro sensor 19”), an acceleration sensor 20 thatgenerates outputs based on longitudinal accelerations of the waist 3(hereinafter referred to as “the waist longitudinal acceleration sensor20”), and an acceleration sensor 21 that generates outputs based onvertical accelerations of the waist 3 (hereinafter referred to as “thewaist vertical acceleration sensor 21”) are integrally mounted andsecured to the waist 3 of the torso 5 through the intermediary of asecuring means, such as a belt, which is not shown.

More technically, the waist longitudinal acceleration sensor 20 is asensor that detects the longitudinal accelerations in the direction of ahorizontal section of the waist 3 (the direction orthogonal to the axisof the waist 3), as in the case of the chest longitudinal accelerationsensor 15. More technically, the waist vertical acceleration sensor 21is a sensor that detects vertical accelerations in the axial directionof the waist 3 (this is orthogonal to the accelerations detected by thewaist longitudinal acceleration sensor 20). The waist longitudinalacceleration sensor 20 and the waist vertical acceleration sensor 21 maybe integrally constructed by a biaxial acceleration sensor.

Further, attached to the hip joint 8 and the knee joint 10 of each leg 2are a hip joint angle sensor 22 and a knee joint angle sensor 23 thatgenerate outputs based on bending angles Δθc and Δθd, respectively,thereof. Regarding the hip joint angle sensor 22, FIG. 2 shows only thehip joint angle sensor 22 related to the hip joint 8 of the leg 2 on thefront side (on the right side, as observed in the forward direction fromthe human being 1); however, another hip joint angle sensor 22 isattached concentrically with the hip joint angle sensor 22 on the frontside to the hip joint 8 of the leg 2 on the other side (on the leftside, as observed in the forward direction from the human being 1).

These angle sensors 22 and 23 are composed of, for example,potentiometers, and mounted on each leg 2 through the intermediary of ameans, such as a band member, which is not shown. Here, in the exampleof the present embodiment, the bending angle Δθc detected by each hipjoint angle sensor 22 is, more technically, the rotational angle aboutthe hip joint 8 of the thigh 9 of each leg 2 with respect to the waist 3(about the axis of the hip joint 8 in the lateral direction of the humanbeing 1), this being based on when the posture relationship between thewaist 3 and the thigh 9 of each leg 2 indicates a predetermined posturerelationship (e.g., the posture relationship in which the axis of thewaist 3 and the axis of the thigh 9 are substantially parallel, as inthe state wherein the human being 1 is upright and stationary).Similarly, the bending angle Δθd detected by each knee joint anglesensor 23 is the rotational angle about the knee joint 10 of the crus 11relative to the thigh 9 (about the axis of the knee joint 10 in thelateral direction of the human being 1), this being based on when theposture relationship between the thigh 9 and the crus 11 of each leg 2indicates a predetermined posture relationship (e.g., the posturerelationship in which the axis of the thigh 9 and the axis of the crus11 are substantially parallel). The axis of the thigh 9 is a straightline connecting the center of the joint (hip joint 8) at one end of thethigh 9 and the center of the joint (knee joint 10) at the other endthereof. Similarly, the axis of the crus 11 is a straight lineconnecting the centers of the joints (the knee joint 10 and the anklejoint 12) at both ends thereof.

Furthermore, at two places on the bottom surface of the foot 13 of eachleg 2, ground contact sensors 51 f and 51 r for detecting contact or nocontact of the places with the ground are installed. More specifically,the ground contact sensors 51 f and 51 r are attached to the shoe soleof each foot 13, the shoe being worn by the human being 1. In this case,the ground contact sensors 51 f and 51 r of each foot 13 are providedlongitudinally apart from each other at a place directly below themetatarsophalangeal joint 13 a (indicated by a dark dot in FIG. 2,hereinafter being referred to as “the MP joint 13 a”) of the foot 13 anda place directly below the ankle joint 12, respectively, and they outputON/OFF signals on the basis of contact or no contact of the respectiveplaces with the ground. More technically, the MP joint 13 a is the jointof the thumb root of the foot 13. The place directly below the MP joint13 a means, more precisely, a place vertically below the MP joint 13 ain a state wherein the human being 1 is in a substantially uprightposture (upright stationary state) with substantially the entire bottomsurface of the foot 13 in contact with a flat floor surface. The sameapplies to the place directly below the ankle joint 12. In the followingexplanation, the ground contact sensor 51 f may be referred to as thedirectly below MP ground contact sensor 51 f, and the ground contactsensor 51 r, as the directly below ankle ground contact sensor 51 r.

The aforesaid sensors 14, 15, 19 to 23, 51 f, and 51 r are connected tothe arithmetic processing unit 16 through signal lines, which are notshown, to input their outputs to the arithmetic processing unit 16. Inassociation with the method of estimating floor reaction force actingpoints in accordance with the present invention, the directly below MPground contact sensor 51 f and the directly below ankle ground contactsensor 51 r correspond to the second ground contact sensor and the firstground contact sensor, respectively. Further, in association with thejoint moment estimating method in accordance with the present invention,the sensors 14, 15, 19 and 20 mean body inclination sensors fordetecting the inclination angles of the body of the human being 1 as abiped walking mobile body, and the sensors 20 and 21 mean sensors fordetecting the accelerations of the waist 3 as a particular part of thehuman being 1 (the biped walking mobile body).

In FIG. 2, the components marked with reference numerals 24 are anklejoint angle sensors that output signals based on the bending angles ofthe ankle joint 12 of each leg 2, and are related to the secondembodiment, which will be discussed later. In the present embodiment(the first embodiment), the ankle joint angle sensors 24 are unnecessaryand not actually provided.

The arithmetic processing unit 16 is equipped with the functional meansshown in FIG. 3. In FIG. 3, the parenthesized portion (the portion ofthe ankle joint angle sensor 24) and the portion indicated by the chaindouble-dashed line are related to the second embodiment to be discussedlater, and these parenthesized portion and the portion indicated by thechain double-dashed line are unnecessary. Therefore, in the followingexplanation of the arithmetic processing unit 16 in the presentembodiment, nothing related to these parenthesized portion and theportion enclosed by the chain double-dashed line will be referred to.

As shown in FIG. 3, the arithmetic processing unit 16 in the presentembodiment is equipped with a leg motion determining means 25 that usesthe detection data of the ground contact sensors 51 r and 51 f so as todetermine whether the motion states of the legs 2, 2 of the human being1 are in the single stance state (the state shown in FIG. 1 (a)) or thedouble stance state (the state shown in FIG. 1 (b)). The arithmeticprocessing unit 16 is further provided with a chest inclination anglemeasuring means 26 that uses the detection data of the chestlongitudinal acceleration sensor 15 and the chest gyro sensor 14 therebyto measure an inclination angle θa in an absolute coordinate system Cfof the chest 4 (specifically, the inclination angle θa with respect to avertical direction: refer to FIG. 2) and a waist inclination anglemeasuring means 27 that uses the detection data of the waistlongitudinal acceleration sensor 20 and the waist gyro sensor 19 so asto measure an inclination angle θb in an absolute coordinate system Cfof the waist 3 (specifically, the inclination angle θb relative to avertical direction: refer to FIG. 2).

The arithmetic processing unit 16 is further provided with a referenceacceleration measuring means 28 that uses the detection data of thewaist longitudinal acceleration sensor 20 and the waist verticalacceleration sensor 21 and the data of the inclination angle θb of thewaist 3 measured by the waist inclination angle measuring means 27 so asto determine an acceleration (translational acceleration) a₀=^(T)(a₀x,a₀z) in the absolute coordinate system Cf at an origin O of a bodilycoordinate system Cp (the xz-coordinate system in FIG. 2) set at thewaist 3, as shown in FIG. 2, as the reference point of the human being 1in the present embodiment. Here, the bodily coordinate system Cp is, tobe more specific, a coordinate system, for example, that has a midpointof a line connecting centers of the right and left hip joints 8, 8,respectively, of the human being 1 defined as the origin O, a verticaldirection being defined as a z-axis direction, and a forward horizontaldirection of the human being 1 defined as an x-axis direction. Thedirections of the three axes are the same as those in the aforesaidabsolute coordinate system Cf.

The arithmetic processing unit 16 is further provided with a leg posturecalculating means 29 that uses detection data of the hip joint anglesensor 22 and the knee joint angle sensor 23 of each leg 2 and the dataof the inclination angle θb of the waist 3 obtained by the waistinclination angle measuring means 27 thereby to determine inclinationangles θc and θd of the thigh 9 and the crus 11, respectively, of eachleg 2 in an absolute coordinate system Cf (specifically, inclinationangles θc and θd relative to a vertical direction: refer to FIG. 2).

The arithmetic processing unit 16 is further provided with a means 30for calculating the position of the center of gravity of each portion byusing data of an inclination angle θa of the chest 4, an inclinationangle θb of the waist 3, and an inclination angle θc of the thigh 9 andan inclination angle θd of the crus 11 of each leg 2, which are obtainedby the chest inclination angle measuring means 26, the waist inclinationangle measuring means 27, and the leg posture calculating means 29, todetermine the position of the center of gravity of each rigidcorresponding part of the human being 1 associated with a rigid linkmodel to be discussed hereinafter (specifically, the position of thecenter of gravity of each rigid corresponding part in the bodilycoordinate system Cp), a bodily center of gravity position calculatingmeans 31 that uses the data of the position of the center of gravity ofthe aforesaid rigid corresponding part so as to determine the positionof the center of gravity of the entire human being 1 in the bodilycoordinate system Cp, an ankle position calculating means 32 that usesthe data of the inclination angles θc and θd of each of the thigh 9 andthe crus 11 of each leg 2 obtained by the leg posture calculating means29 so as to determine the position of the ankle joint 12 of each leg 2in the bodily coordinate system Cp, and further uses the data of theposition of the center of gravity G0 of the entire human being 1 (referto FIG. 1: hereinafter referred to as “the bodily center of gravity G0”) obtained by the bodily center of gravity position calculating means31 to determine the position of the ankle joint 12 of the leg 2 relativeto the bodily center of gravity G0 (specifically, ΔXf, ΔZf, ΔXr and ΔZrin the above Equation (5)), an MP position calculating means 33 thatuses the data of the position of the ankle joint 12 (the position in thebodily coordinate system Cp) obtained by the ankle position calculatingmeans 32 to determine the position (specifically, the position in thex-axis direction) of an MP joint 13 a of the foot 13 of each leg 2 inthe bodily coordinate system Cp, and a bodily center of gravityacceleration calculating means 34 that uses the data of the position ofthe bodily center of gravity G0 obtained by the bodily center of gravityposition calculating means 31 and the data of the acceleration a₀ at theorigin O of the bodily coordinate system Cp obtained by the referenceacceleration measuring means 28 thereby to determine an accelerationa=^(T)(ax, az)(refer to FIG. 1) of the bodily center of gravity G0 inthe absolute coordinate system Cf.

The arithmetic processing unit 16 is further provided with a means 35for calculating the acceleration of each portion of a leg by using thedata of the position of the center of gravity of each rigidcorresponding part of the human being 1 (specifically, the position ofthe center of gravity of a rigid corresponding part related to the leg2) obtained by the means 30 for calculating the position of the centerof gravity of each portion and the data of the acceleration a₀ at theorigin O of the bodily coordinate system Cp obtained by the referenceacceleration measuring means 28 so as to determine the acceleration(translational acceleration) of the center of gravity of the thigh 9 andthe crus 11 of each leg 2 in the absolute coordinate system Cf, a means36 for calculating the angular acceleration of each portion of a leg byusing the data of the inclination angles θc and θd of the thigh 9 andthe crus 11 of each leg 2 obtained by the leg posture calculating means29 to determine the angular accelerations of the thigh 9 and the crus 11of the legs 2, 2 in the absolute coordinate system Cf, and a floorreaction force acting point estimating means 38 for estimating theposition of a floor reaction force acting point of each leg 2 in contactwith the ground on the basis of the bodily center of gravity G0 , thepositions of the ankle joint 12 and the MP joint 13 a (the positions inthe bodily coordinate system Cp) determined by the bodily center ofgravity position calculating means 31, the ankle position calculatingmeans 32, and the MP position calculating means 33, respectively, anddetection outputs of the ground contact sensors 51 f and 51 r of eachleg 2.

The arithmetic processing unit 16 is further provided with a floorreaction force estimating means 39 for determining the estimated valueof a floor reaction force acting on each leg 2 by using the data of theacceleration a of the bodily center of gravity determined by the bodilycenter of gravity acceleration calculating means 34, the data of theposition of the ankle joint 12 of each leg 2 relative to the bodilycenter of gravity G0 determined by the ankle position calculating means32, and the data of the determination result of the motion state of theleg 2 given by the leg motion determining means 25, and a joint momentestimating means 40 for estimating moments acting on the knee joint 10and the hip joint 8 of each leg 2 by using this data of the estimatedvalue of the floor reaction force, the data of the accelerations of thecenters of gravity of the thigh 9 and the crus 11 of each leg 2 obtainedby the means 35 for calculating the acceleration of each portion of aleg, the data of the angular accelerations of the thigh 9 and the crus11 of each leg 2 obtained by the means 36 for calculating the angularacceleration of each portion of a leg, the data of the estimatedposition of a floor reaction force acting point obtained by the floorreaction force acting point estimating means 38, and the data of theinclination angles θc and θd of the thigh 9 and the crus 11,respectively, of each leg 2 obtained by the leg posture calculatingmeans 29.

An operation of the present embodiment will be explained in combinationwith more detailed description of the processing by each means of theaforementioned arithmetic processing unit 16.

In the present embodiment, when, for example, the human being 1 performsa motion of the legs 2, such as walking, if a power switch, not shown,of the arithmetic processing unit 16 is turned on while both legs 2 and2 are in contact with a floor (while both feet 13 and 13 are in contactwith the ground), then processing is successively carried out by thearithmetic processing unit 16 at a predetermined cycle time, asexplained below, thereby successively determining estimated values orthe like of floor reaction forces acting on each leg 2.

More specifically, the arithmetic processing unit 16 first executes theprocessing of the leg motion determining means 25. In the processing ofthe leg motion determining means 25, ON/OFF of the ground contactsensors 51 f and 51 r of each leg 2 is determined for each cycle timedescribed above. And, if at least one of the ground contact sensors 51 fand 51 r of one leg 2 outputs an ON signal (the place of one of theground contact sensors 51 f and 51 r is in contact with the ground) andif at least one of the ground contact sensors 51 f and 51 r of the otherleg 2 outputs the ON signal, then it is determined that the motion modeof the legs 2, 2 of the human being 1 is the double stance state shownin FIG. 1 (b) mentioned above. Further, if at least one of the groundcontact sensors 51 f and 51 r of one leg 2 outputs the ON signal and ifnone of the ground contact sensors 51 f and 51 r of the other leg 2output the ON signal (the places of both ground contact sensors 51 f and51 r are not in contact with the ground), then it is determined that themotion mode of the legs 2, 2 of the human being 1 is the single stancestate shown in FIG. 1 (a) mentioned above.

Whether it is the single stance state or the double stance state may bedetermined solely by the detection signals of the ground contact sensors51 f and 51 r as described above. During a transition between the singlestance state and the double stance state, the determination may beperformed by considering also a change or the like in detection outputof the waist vertical acceleration sensor 21.

In parallel to the processing of the leg motion determining means 25 asdescribed above, the arithmetic processing unit 16 carries out theprocessing of the chest inclination angle measuring means 26 and thewaist inclination angle measuring means 27. In this case, the processingby the chest inclination angle measuring means 26 successivelydetermines the inclination angle θa of the chest 4 in the absolutecoordinate system Cf at each cycle time mentioned above by a publiclyknown technique based on the so-called Kalman filter processing, usingthe detection data of the longitudinal accelerations of the chest 4 andthe angular velocity of the chest 4 received from the chest longitudinalacceleration sensor 15 and the chest gyro sensor 14. Similarly, theprocessing by the waist inclination angle measuring means 27successively determines the inclination angle θb of the waist 3 in theabsolute coordinate system Cf by using the Kalman filter processing fromthe detection data of the longitudinal accelerations of the waist 3 andthe angular velocity of the waist 3 received from the waist longitudinalacceleration sensor 20 and the waist gyro sensor 19, respectively. Here,the inclination angles θa and θb of the chest 4 and the waist 3,respectively, in the absolute coordinate system Cf denote inclinationangles with respect to, for example, the vertical direction(gravitational direction) in the present embodiment.

The inclination angles of the chest 4 and the waist 3 can bealternatively determined by, for example, integrating the detection dataof angular velocities obtained by the gyro sensors 14 and 19. However,performing the Kalman filter processing, as in the present embodiment,allows the inclination angles θa and θb of the chest 4 and the waist 3to be measured with high accuracy.

Next, the arithmetic processing unit 16 performs processing of the legposture calculating means 29 and the processing of the referenceacceleration measuring means 28.

In the processing implemented by the leg posture calculating means 29,the inclination angles θc and θd (inclination angles with respect to thevertical direction: refer to FIG. 2) of the thigh 9 and the crus 11 ofeach leg 2 are determined at each cycle time, as described below. Theinclination angle θc of the thigh 9 of each leg 2 is calculatedaccording to Equation (6) given below on the basis of the current valueof the detection data of the bending angle Δθc of the hip joint 8obtained by the hip joint angle sensor 22 attached to the leg 2 and thecurrent value of the inclination angle θb of the waist 3 determined bythe waist inclination angle measuring means 27:θc=θb+Δθc  (6)

where the inclination angle θb of the waist 3 takes a negative value ifthe waist 3 inclines with respect to the vertical direction such that anupper end portion of the waist 3 juts out farther to the front side ofthe human being 1 than a lower end portion thereof; and the bendingangle Δθc of the hip joint 8 takes a positive value if the thigh 9inclines with respect to the axis of the waist 3 such that a lower endportion of the thigh 9 juts out toward the front side of the human being1.

Furthermore, the inclination angle θd of the crus 11 of each leg 2 iscalculated according to Equation (7) given below on the basis of thecurrent value of the inclination angle θc of the thigh 9 determined asdescribed above and the current value of the detection data of thebending angle Δθd of the knee joint 10 obtained by the knee joint anglesensor 23 attached to the leg 2:θd=θc−Δθd  (7)

where the bending angle of the knee joint 10 takes a positive value ifthe crus 11 inclines toward the rear side of the thigh 9 with respect tothe axis of the thigh 9.

In the processing of the reference acceleration measuring means 28, theacceleration a₀=^(T)(a₀x, a₀z) in the absolute coordinate system Cf ofthe origin O of the bodily coordinate system Cp is determined asdescribed below. If the current value of the detection data of alongitudinal acceleration of the waist 3 obtained from the waistlongitudinal acceleration sensor 20 is denoted by a_(p), and the currentvalue of the detection data of the vertical acceleration of the waist 3obtained from the waist vertical acceleration sensor 21 is denoted bya_(q), then the acceleration a₀=^(T)(a₀x, a₀z) in the absolutecoordinate system Cf is determined according to Equation (8) given belowfrom the detection data a_(p) and a_(q) and the current value of theinclination angle θb of the waist 3 obtained by the waist inclinationangle measuring means 27:

$\quad\begin{matrix}\begin{matrix}{a_{0} = {\,^{T}( {{a_{0}x},{a_{0}z}} )}} \\{= {\,^{T}( {{{{a_{p} \cdot \cos}\;\theta\; b} - {{a_{q} \cdot \sin}\;\theta\; b}},{{{a_{p} \cdot \sin}\;\theta\; b} +}} }} \\ {{{a_{q} \cdot \cos}\;\theta\; b} - g} )\end{matrix} & (8)\end{matrix}$

The arithmetic processing unit 16 then carries out the processing of themeans 30 for calculating the position of the center of gravity of eachportion to determine the position of the center of gravity of each rigidcorresponding part of the human being 1 in the bodily coordinate systemCp (the position relative to the origin of the bodily coordinate systemCp), using a rigid link model explained below.

As shown in FIG. 4, a rigid link model R used in the present embodimentis a model representing the human being 1 by connecting rigid bodies R1,R1 corresponding to the thighs 9 of the respective legs 2, rigid bodiesR2, R2 corresponding to the cruses 11, a rigid body R3 corresponding tothe waist 3, and a rigid body R4 corresponding to a portion 38 combiningthe chest 4, the arms 7, 7, and the head 6 (hereinafter referred to as“the body 38”). In this case, the connection of the respective rigidbodies R1 and the rigid body R3 and the connection of the rigid bodiesR1 and the rigid bodies R2 correspond to the hip joints 8 and the kneejoints 10, respectively. In addition, the connection of the rigid bodyR3 and the rigid body R4 provides a tilt supporting point 39 of thechest 4 with respect to the waist 3.

In the present embodiment, the positions of the centers of gravity G1 ,G2 , G3 and G4 of the rigid corresponding parts (the thighs 9 and thecruses 11 of the respective legs 2, the waist 3, and the body 38) of thehuman being 1 associated with the rigid bodies R1 to R4 of the rigidlink model R in the rigid corresponding parts are determined beforehandand stored in a memory, not shown, of the arithmetic processing unit 16.

The positions of the centers of gravity G1 , G2 , G3 and G4 of the rigidcorresponding parts that have been stored and retained in the arithmeticprocessing unit 16 are the positions in a coordinate system fixed withrespect to the rigid corresponding parts. In this case, as examples ofdata indicating the positions of the centers of gravity G1 , G2 , G3 andG4 of the rigid corresponding parts, the distances in the axialdirection of the rigid corresponding parts from the midpoints of jointsat one end of each of the rigid corresponding parts are used.Specifically, for example, the position of the center of gravity G1 ofeach thigh 9 is indicated as the position at a distance t1 in the axialdirection of the thigh 9 from the center of the hip joint 8 of the thigh9, and the position of the center of gravity G2 of each crus 11 isindicated as the position at a distance t2 in the axial direction of thecrus 11 from the center of the knee joint 10 of the crus 11, as shown inFIG. 4. The values of the distances t1 and t2 are determined beforehandand retained in a memory in the arithmetic processing unit 16. The sameapplies to the positions of the centers of gravity G3 and G4 of otherrigid corresponding parts.

Technically speaking, the position of the center of gravity G4 of thebody 38 is subject to influences of motions of the arms 7 and 7 includedin the body 38. In a walking mode, the arms 7 and 7 are generallypositionally symmetrical with respect to the axis of the chest 4, sothat the position of the center of gravity G4 of the body 38 does notchange much, and becomes substantially the same as the position of thecenter of gravity G4 of the body 38 in, for example, an uprightstationary state.

According to the present embodiment, in addition to the data indicatingthe positions of the centers of gravity G1 , G2 , G3 and G4 of the rigidcorresponding parts (the thighs 9 and the cruses 11 of the legs 2, thewaist 3, and the body 38), the data of weights of the rigidcorresponding parts and the data of sizes of the rigid correspondingparts (e.g., data of lengths of the rigid corresponding parts) aredetermined beforehand and retained in a memory in the arithmeticprocessing unit 16.

The weight of the crus 11 includes the weight of the foot 13. Asdescribed above, the data to be stored and retained in the arithmeticprocessing unit 16 beforehand may be determined by actual measurement orthe like, or may be estimated on the basis of human average statisticdata from height and weight of the human being 1. Generally, thepositions of the centers of gravity G1 , G2 , G3 and G4 , the weightsand sizes of the rigid corresponding parts are correlated with theheight and weight of a human being. Based on the correlation, from theheight and weight of the human being, the positions of the centers ofgravity G1 , G2 , G3 and G4 , the weights, and sizes of the rigidcorresponding parts can be estimated with relatively high accuracy.

The means 30 for calculating the position of the center of gravity ofeach portion uses the data stored and retained beforehand in thearithmetic processing unit 16, as described above, the current values ofthe inclination angle θa of the chest 4 (=the inclination angle of thebody 38) and the inclination angle θb of the waist 3 determined by thechest inclination angle measuring means 26 and the waist inclinationangle measuring means 27, respectively, and the current values of theinclination angles θc and θd of the thigh 9 and the crus 11 of each leg2 determined by the leg posture calculating means 29 so as to determinethe positions of the centers of gravity G1 , G2 , G3 and G4 of the rigidcorresponding parts in the bodily coordinate system Cp (thexz-coordinate system shown in FIG. 4) having the origin O fixed on thewaist 3.

In this case, the inclination angles θa to θd of the rigid correspondingparts (the thighs 9 and the cruses 11 of the legs 2, the waist 3, andthe body 38) have been determined, as described above; therefore, thepositions and postures of the rigid corresponding parts in the bodilycoordinate system Cp are obtained from the data of the inclinationangles θa to θd and the data of the sizes of the rigid correspondingparts. Thus, the positions of the centers of gravity G1 , G2 , G3 and G4of the rigid corresponding parts in the bodily coordinate system Cp canbe determined.

Specifically, referring to, for example, FIG. 4, regarding the leg 2positioned on the left side in FIG. 4, the inclination angle of thethigh 9 in the bodily coordinate system Cp (the inclination anglerelative to the z-axis direction) is θc (in this case, θc<0 in FIG. 4);hence, the coordinate of the position of the center of gravity G1 of thethigh 9 in the bodily coordinate system Cp is (t1·sin θc, −t1·cos θc).The inclination angle in the bodily coordinate system Cp of the crus 11is θd (θd<0 in FIG. 4); therefore, if the length of the thigh 9 isdenoted by Lc, then the coordinate of the position of the center ofgravity G2 of the crus 11 in the bodily coordinate system Cp will be(Lc·sin θc+t2·sin θd, −Lc·cos θc−t2·cos θd). The centers of gravity ofthe thigh 9 and the crus 11 of the other leg 2, and of the waist 3 andthe body 38 are determined in the same manner as described above.

After determining the positions of the centers of gravity G1 , G2 , G3and G4 of the rigid corresponding parts in the bodily coordinate systemCp by the means 30 for calculating the position of the center of gravityof each portion, the arithmetic processing unit 16 executes theprocessing by the bodily center of gravity position calculating means 31to determine the position (xg, zg) of the bodily center of gravity G0 ofthe human being 1 in the bodily coordinate system Cp, using the data ofthe positions of the centers of gravity G1 , G2 G2 , G3 and G4 of therigid corresponding parts and the data of the weights of the rigidcorresponding parts.

If the position of the center of gravity G3 and the weight of the waist3 in the bodily coordinate system Cp are denoted by (x3, z3) and m3,respectively, the position of the center of gravity G4 and the weight ofthe body 38 are denoted by (x4, z4) and m4, respectively, the positionof the center of gravity G1 and the weight of the thigh 9 of the leg 2,which is located at left as observed in the advancing direction of thehuman being 1, are denoted by (x1L, z1L) and m1L, respectively, theposition of the center of gravity G2 and the weight of the crus 11 ofthe leg 2 are denoted by (x2L, z2L) and m2L, respectively, the positionof the center of gravity G1 and the weight of the thigh 9 of the leg 2at right are denoted by (x1R, z1R) and m1R, respectively, the positionof the center of gravity G2 and the weight of the crus 11 of the leg 2are denoted by (x2R, z2R) and m2R, respectively, and the weight of thehuman being 1 is denoted by M (=m1L+m2L+m1R+m2R+m3+m4), then theposition (xg, zg) of the bodily center of gravity G0 of the human being1 in the bodily coordinate system Cp will be determined by Equation (9)given below:

$\quad\begin{matrix}{\begin{matrix}{{xg} = ( {{m\; 1{L \cdot x}\; 1L} + {m\; 1{R \cdot x}\; 1R} + {m\; 2{L \cdot x}\; 2L} +} } \\{ {{m\; 2{R \cdot x}\; 2R} + {m\;{3 \cdot x}\; 3} + {m\;{4 \cdot x}\; 4}} )/M}\end{matrix}\begin{matrix}{{zg}\; = ( {{m\; 1\;{L \cdot z}\; 1\; L}\; + \;{m\; 1\;{R \cdot z}\; 1\; R}\; + \;{m\; 2\;{L \cdot z}\; 2\; L}\; +}\; } \\{ {{m\; 2\;{R \cdot z}\; 2\; R}\; + \;{m\;{3 \cdot z}\; 3}\; + \;{m\;{4 \cdot z}\; 4}} )/M}\end{matrix}} & (9)\end{matrix}$

After carrying out the processing of the bodily center of gravityposition calculating means 31, the arithmetic processing unit 16 furthercarries out the processing of the bodily center of gravity accelerationcalculating means 34, the processing of the ankle position calculatingmeans 32, and the processing of the MP position calculating means 33.

In this case, in the processing of the bodily center of gravityacceleration calculating means 34, first, the two-level differentialvalue of the position (xg, zg) of the bodily center of gravity G0 in thebodily coordinate system Cp, that is, the acceleration ^(T)(d²xg/dt²,d²zg/dt²) of the bodily center of gravity G0 with respect to the originO of the bodily coordinate system Cp, is determined, using thetime-series data of the position (xg, zg) of the bodily center ofgravity G0 in the bodily coordinate system Cp determined by the bodilycenter of gravity position calculating means 31 for each cycle timementioned above. Then, a vector sum of the acceleration ^(T)(d²xg/dt²,d²zg/dt²) and the acceleration a₀=^(T)(a₀x, a₀z) in the absolutecoordinate system Cf of the origin O of the bodily coordinate system Cpdetermined by the reference acceleration measuring means 28 isdetermined, thereby determining an acceleration a=^(T)(ax, az) of thebodily center of gravity G0 in the absolute coordinate system Cf.

In the processing of the ankle position calculating means 32, first, theposition of the ankle joint 12 of each leg 2 in the bodily coordinatesystem Cp is determined by the same processing as that of the means 30for calculating the position of the center of gravity of each portionfrom the current values of the data of the inclination angles θc and θdof the thigh 9 and the crus 11 of each leg 2 determined by the legposture calculating means 29, the current value of the data of theinclination angle θb of the waist 3 determined by the waist inclinationangle measuring means 27, and the data of the sizes (lengths) of thethigh 9 and the crus 11. Specifically, referring to FIG. 4, regardingthe leg 2 located on the left side in FIG. 4, if the length of the crus11 (the length from the center of the knee joint 10 to the center of theankle joint 12) is denoted by Ld, then the coordinate (x12, z12) of theposition of the ankle joint 12 in the bodily coordinate system Cp willbe (Lc·sin θc+Ld·sin θd, −Lc·cos θc−Ld·cos θd)(where θc<0, θd<0 in FIG.4). The same applies to the other leg 2.

Furthermore, the positional vector ^(T)(x12−xg, z12−zg) of the ankle 12of each leg 2 with respect to the bodily center of gravity G0 , that is,ΔXf, ΔZf, ΔXr and ΔZr in the above Equation (5), is determined from theposition (x12, z12) in the bodily coordinate system Cp of the anklejoint 12 and the current value of the data of the position (xg, zg) ofthe bodily center of gravity G0 in the bodily coordinate system Cpdetermined by the bodily center of gravity position calculating means31.

In the processing of the MP position calculating means 33, the positionof the MP joint 13 a (more specifically, the position in the x-axisdirection in the bodily coordinate system Cp) is determined as follows.Referring to FIG. 5, in the present embodiment, a distance Δxmp0 in thehorizontal direction (the x-axis direction) between the ankle joint 12and the MP joint 13 a in the state wherein the human being 1 is uprightstationary (in the state wherein the human being 1 is standing uprighton a horizontal floor A, having substantially the entire surface of thesole of the foot 14 of each leg 2 in contact with the floor A) isactually measured beforehand and retained in a memory in the arithmeticprocessing unit 16. The distance Δxmp0 may be actually measured andretained in a memory separately for each leg 2, or it may be actuallymeasured only on one leg 2 and shared for both legs 2 and 2.

In general, the horizontal distance between the ankle joint 12 and theMP joint 13 a while the human being 1 is in motion, such as level-groundwalking, is approximately equal to the aforesaid distance Δxmp0 in theupright stationary state of the human being 1. Accordingly, in thepresent embodiment, the position (the position in the x-axis direction)of the MP joint 13 a is determined as the position apart from the anklejoint 12 by the aforesaid distance Δxmp0 in the x-axis direction.Specifically, the value obtained by adding the distance Δxmp0 to anx-axis coordinate component x12 of the current value of the position(x12, z12) of the ankle joint 12 in the bodily coordinate system Cpobtained by the ankle position calculating means 32 is determined as theposition of the MP joint 13 a in the x-axis direction in the bodilycoordinate system Cp.

Next, the arithmetic processing unit 16 executes the processing of thefloor reaction force acting point estimating means 38 and the processingof the floor reaction force estimating means 39. In the processing ofthe floor reaction force acting point estimating means 38, a floorreaction force acting point related to each leg 2 in contact with theground (the point at which total floor reaction force acting on anin-contact-with-the-ground place of the foot 13 is considered toconcentrate) is estimated as described below. First, detection signalsof the ground contact sensors 51 f and 51 r of each leg 2 aredetermined, and if one of the ground contact sensors 51 f and 51 routputs an ON signal, then it is determined that the leg 2 is in contactwith the ground. And, on the leg 2 in contact with the ground, theposition of a floor reaction force acting point in the x-axis direction(the horizontal position in the advancing direction of the human being1) is determined on the basis of the combination of ON/OFF of the groundcontact sensors 51 f and 51 r of the leg 2 and the relative positionalrelationship (specifically, the relative positional relationship in thex-axis direction) among the ankle joint 12 and the MP joint 13 a of theleg 2 and the bodily center of gravity G0.

More detailedly, referring to FIG. 6 (a), if the directly below ankleground contact sensor 51 r outputs an ON signal, whereas the directlybelow MP ground contact sensor 51 f is OFF, then it is regarded that afloor reaction force acting point exists vertically immediately belowthe ankle joint 12, and the position of the ankle joint 12 in the x-axisdirection is determined as the position of the floor reaction forceacting point in the x-axis direction (the horizontal position in theadvancing direction of the human being 1). This means that the statewherein the directly below ankle ground contact sensor 51 r and thedirectly below MP ground contact sensor 51 f are ON and OFF,respectively, as described above is a state wherein the foot 13 of theleg 2 provided with the ground contact sensors 51 r and 51 f is incontact with a floor A at a place adjacent to the heel thereof. And, insuch a state, the floor reaction force acting point of the leg 2 ispositioned substantially right below (vertically below) the ankle joint12. Thus, if the directly below ankle ground contact sensor 51 r and thedirectly below MP ground contact sensor 51 f are ON and OFF,respectively, then the position of the floor reaction force acting pointin the x-axis direction of the leg 2 in contact with the ground isdetermined as described above. FIG. 6 (a) schematically shows only oneleg 2 in contact with the ground, and the other leg is not shown. Thesame will apply to FIG. 6 (b) and FIGS. 7 (a) to (c) to be explainedbelow.

Further, referring to FIG. 6 (b), if the directly below ankle groundcontact sensor 51 r is OFF, whereas the directly below MP ground contactsensor 51 f outputs an ON signal, then it is regarded that a floorreaction force acting point exists vertically immediately below the MPjoint 13 a, and the position of the MP joint 13 a in the x-axisdirection is determined as the position of the floor reaction forceacting point in the x-axis direction. This means that the state whereinthe directly below ankle ground contact sensor 51 r and the directlybelow MP ground contact sensor 51 f are OFF and ON, respectively, is astate wherein the foot 13 of the leg 2 provided with the ground contactsensors 51 r and 51 f is in contact with the floor A at a place adjacentto the toe thereof. And, in such a state, the floor reaction forceacting point of the leg 2 is positioned substantially right below(vertically below) the MP joint 13 a. Thus, if the directly below ankleground contact sensor 51 r and the directly below MP ground contactsensor 51 f are OFF and ON, respectively, then the position of the floorreaction force acting point in the x-axis direction of the leg 2 incontact with the ground is determined as described above.

The method for estimating the position of a floor reaction force actingpoint in the x-axis direction in the case of the combination of ON/OFFof the ground contact sensors 51 r and 51 f corresponding to FIGS. 6 (a)and (b), respectively, does not depend on the mutual positionalrelationship among the bodily center of gravity G0, the ankle joint 12,and the MP joint 13 a.

Meanwhile, if both the directly below ankle ground contact sensor 51 rand the directly below MP ground contact sensor 51 f output ON signals,then the position of a floor reaction force acting point in the x-axisdirection is further estimated on the basis of the relative positionalrelationship among the bodily center of gravity G0, the ankle joint 12,and the MP joint 13 a (specifically, the relative positionalrelationship in the x-axis direction of the bodily coordinate systemCp). More detailedly, if the bodily center of gravity G0 is positionedbehind the ankle joint 12 (if the ankle joint 12 is positioned beforethe bodily center of gravity G0) as shown in FIG. 7 (a), then it isassumed that the floor reaction force acting point exists verticallydirectly below the ankle joint 12, and the position of the ankle joint12 in the x-axis direction is determined as the position of the floorreaction force acting point in the x-axis direction. In other words, ina state wherein the ankle joint 12 of a leg 2 in contact with the groundis located before the bodily center of gravity G0, the floor reactionforce related to the leg 2 is concentrated in a place adjacent to theheel of the foot 13. In such a state, the floor reaction force actingpoint of the leg 2 is positioned substantially directly below the anklejoint 12. Hence, if the ankle joint 12 is positioned before the bodilycenter of gravity G0, as shown in FIG. 7 (a), the x-axis position of thefloor reaction force acting point of the leg 2 in contact with theground is determined as described above.

Further, if the bodily center of gravity G0 is located between the MPjoint 13 a and the ankle joint 12 in the x-axis direction as shown inFIG. 7 (b), then it is assumed that the floor reaction force actingpoint exists vertically directly below the bodily center of gravity G0,and the position of the bodily center of gravity G0 in the x-axisdirection is determined as the position of the floor reaction forceacting point in the x-axis direction. This means that if the position ofthe bodily center of gravity G0 in the x-axis direction is between theMP joint 13 a and the ankle joint 12 of the leg 2 in contact with theground, the floor reaction force related to the leg 2 concentrates inthe vicinity of a spot vertically below the bodily center of gravity G0.Thus, if the position of the bodily center of gravity G0 in the x-axisdirection is between the MP joint 13 a and the ankle joint 12 of the leg2 in contact with the ground, as shown in FIG. 7 (b), the x-axisposition of the floor reaction force acting point of the leg 2 incontact with the ground is determined as described above.

Further, if the bodily center of gravity G0 is positioned before the MPjoint 13 a (if the MP joint 13 a is positioned behind the bodily centerof gravity G0) as shown in FIG. 7 (c), then it is assumed that the floorreaction force acting point exists vertically directly below the MPjoint 13 a, and the position of the MP joint 13 a in the x-axisdirection is determined as the position of the floor reaction forceacting point in the x-axis direction. In other words, in a state whereinthe MP joint 13 a of a leg 2 in contact with the ground is locatedbehind the bodily center of gravity G0, the floor reaction force relatedto the leg 2 is concentrated in a place adjacent to the toe of the foot13. In such a state, the floor reaction force acting point of the leg 2is positioned substantially directly below the MP joint 13 a. Hence, ifthe MP joint 13 a is positioned behind the bodily center of gravity G0,as shown in FIG. 7 (c), the x-axis position of the floor reaction forceacting point of the leg 2 in contact with the ground is determined asdescribed above.

The x-axis position of the floor reaction force acting point of each leg2 in contact with the ground is estimated by the processing of the floorreaction force acting point estimating means 38 explained above. Therelationship among the combinations of ON and OFF of both ground contactsensors 51 r and 51 f, the relative positional relationship among thebodily center of gravity G0, the ankle joint 12 and the MP joint 13 a,and the position of a floor reaction force acting point in the x-axisdirection obviously applies to a case where the human being 1 is walkingon a flat ground and generally applies also to a case where, forexample, the human being 1 sits onto a chair or rises from the chair,and a case where the human being 1 walks on a staircase or a slope.

Further in the processing of the floor reaction force acting pointestimating means 38, the vertical position (the position in the z-axisdirection) of the floor reaction force acting point of each leg 2 incontact with the ground is determined as described below. First, on eachleg 2 in contact with the ground, the distance between the ankle joint12 of the leg 2 and a ground contact surface (the floor A) is grasped.In this case, according to the present embodiment, a value stored andretained beforehand in the arithmetic processing unit 16 is grasped asthe distance between the ankle joint 12 and the ground contact surface(the floor A)(hereinafter referred to as “the distance between the anklejoint and the ground contact surface”). To be more specific, referringto FIG. 5 mentioned above, a distance Ha from the center of the anklejoint 12 to the floor A surface (the ground contact surface) when thehuman being 1 is in the upright stationary state (hereinafter referredto as “the ankle joint reference height Ha”) is actually measured inadvance and retained in a memory of the arithmetic processing unit 16.The ankle joint reference height Ha may be actually measured for eachleg 2 separately, or only one leg 2 may be actually measured andretained in a memory to be shared for both legs 2. Thus, the ankle jointreference height Ha stored and retained as described above is grasped asthe distance between the ankle joint and the ground contact surface.

As discussed above, the distance between the ankle joint and the groundcontact surface is grasped, and then the vertical position (the positionin the z-axis direction) of a floor reaction force acting point isdetermined as the position vertically apart downward from the positionof the ankle joint 12 by the grasped distance between the ankle jointand the ground contact surface. In other words, the vertical position(the position in the bodily coordinate system Cp) of the floor reactionforce acting point is determined as the value obtained by subtractingthe distance between the ankle joint and the ground contact surface,which has been grasped as described above, from the value of the z-axiscomponent of the position of the ankle joint 12 (the upward directionbeing defined as the positive direction of the z-axis).

According to the present embodiment, in order to calculate a jointmoment by a joint moment estimating means 40, which will be discussedhereinafter, the position of the floor reaction force acting point inthe bodily coordinate system Cp decided as described above(xz-coordinate component) is further converted into a position defined,using the position of the ankle joint 12 in the bodily coordinate systemCp calculated by the ankle position calculating means 32 as itsreference. More specifically, the estimated position of a floor reactionforce acting point is determined by conversion into a positional vectorbased on the position of the ankle joint 12 as the reference(hereinafter referred to as “the floor reaction force acting pointvector”).

By the processing of the floor reaction force acting point estimatingmeans 38 explained above, the floor reaction force acting point vectors(the positions in the x-axis direction and the z-axis direction) basedon the ankle joint 12 are estimated on each leg 2 in contact with theground.

In the processing of the floor reaction force estimating means 39, ifthe motion mode of the leg 2 determined at the current cycle time by theleg motion determining means 25 is the single stance state, then theestimated value of the floor reaction force F=^(T)(Fx, Fz) acting on theleg 2 in contact with the ground is determined according to the aboveEquation (2) from the values of the weight M of the human being land thegravity acceleration g (these are stored in the arithmetic processingunit 16 beforehand) and the current value of the acceleration a=^(T)(ax,az) of the bodily center of gravity G0in the absolute coordinate systemCf determined by the bodily center of gravity acceleration calculatingmeans 34. In this case, the floor reaction force acting on the leg 2 notin contact with the ground (the free leg 2) is ^(T)(0, 0).

If the motion state of the leg 2 determined at the current cycle time bythe leg motion determining means 25 is the double stance state, then theestimated values of the floor reaction forces Ff=^(T)(Ffx, Ffz) andFr=^(T)(Frx, Frz) of the individual legs 2 are determined according tothe above Equation (5) from the weight M of the human being 1 and thegravity acceleration g, the current value of the acceleration a=^(T)(ax,az) of the bodily center of gravity G0in the absolute coordinate systemCf determined by the bodily center of gravity acceleration calculatingmeans 34, and the data of the current values of the positions of theankle joints 12 of the individual legs 2 relative to the bodily centerof gravity G0determined by the ankle position calculating means 32 (thecurrent values of data of ΔXf, ΔZf, ΔXr, and ΔZr of Equation (5)).

Meanwhile, the arithmetic processing unit 16 carries out the processingof the means 35 for calculating the acceleration of each portion of aleg and the means 36 for calculating the angular acceleration of eachportion of a leg in parallel to the processing of the bodily center ofgravity position calculating means 31, the bodily center of gravityacceleration calculating means 34, the ankle position calculating means32, the MP position calculating means 33, the floor reaction forceacting point estimating means 38, and the floor reaction forceestimating means 39 described above.

In this case, in the processing of the means 35 for calculating theacceleration of each portion of a leg, as in the processing of thebodily center of gravity acceleration calculating means 34, first, thetwo-level differential values of the positions of the centers of gravityG1 and G2 of the thigh 9 and the crus 11 in the bodily coordinate systemCp, that is, the accelerations of the centers of gravity G1 and G2 ofthe thigh 9 and the crus 11 in the bodily coordinate system Cp (theaccelerations relative to the origin O of the bodily coordinate systemCp), are determined, using the time-series data of the positions of thecenters of gravity G1 and G2 of the thigh 9 and the crus 11, which arerigid corresponding parts of the legs 2 in the bodily coordinate systemCp determined by the means 30 for calculating the position of the centerof gravity of each portion at each cycle time. Then, the vector sum ofthe aforesaid accelerations and the acceleration a₀=^(T)(a₀x, a₀z) inthe absolute coordinate system Cf of the waist 3 obtained by thereference acceleration measuring means 28 is determined, therebydetermining the accelerations of the thigh 9 and the crus 11,respectively, in the absolute coordinate system Cf (more specifically,the coordinate components of the accelerations in the absolutecoordinate system Cf).

In the processing of the means 36 for calculating the angularacceleration of each portion of a leg, the time series data of theinclination angles θc and θd of the thigh 9 and the crus 11 of each leg2 obtained by the leg posture calculating means 29 for each cycle timeis used to determine the two-level differential values of theinclination angles θc and θd of the thigh 9 and the crus 11, that is,the angular accelerations of the thigh 9 and the crus 11, respectively.

Next, the arithmetic processing unit 16 executes the processing of thejoint moment estimating means 40 to determine the moments acting on theknee joint 10 and the hip joint 8 of each leg 2. This processing iscarried out on the basis of a so-called inverse dynamics model by usingthe current values of the data determined by the floor reaction forceestimating means 39, the means 35 for calculating the acceleration ofeach portion of a leg, the means 36 for calculating the angularacceleration of each portion of a leg, the floor reaction force actingpoint estimating means 38, and the leg posture calculating means 29,respectively. The inverse dynamics model uses an equation of motionrelated to a translational motion and the equation of motion related toa rotational motion of each rigid corresponding part of the human being1 to determine moments acting on joints in order, beginning with a jointclosest to a floor reaction force acting point. In the presentembodiment, the moments acting on the knee joint 10 and the hip joint 8of each leg 2 are determined in order.

To be more specific, referring to FIG. 8, first, regarding the crus 11of each leg 2, the force acting on the ankle joint 12 of the distalportion of the crus 11 (the joint reaction force), the force acting onthe portion of the knee joint 10 of the crus 11 (the joint reactionforce), and the translational acceleration of the center of gravity G2of the crus 11 are denoted by ^(T)(F₁x, F₁z), ^(T)(F₂x, F₂z), and^(T)(a₂x, a₂z), respectively, according to the component notation in theabsolute coordinate system Cf, and the weight of the crus 11 is denotedby m₂. At this time, the equation of motion related to the translationalmotion of the center of gravity G2 of the crus 11 will be the followingequation (10):^(T)(m ₂ ·a ₂ x,m ₂ ·a ₂ z)=^(T)(F ₁ x−F ₂ x,F ₁ z−F ₂ z−m ₂ ·g)therefore,^(T)(F ₂ x,F ₂ z)=T(F ₁ x−m ₂ ·a ₂ x,F ₁ z−m ₂ ·a ₂ z−m ₂ ·g)  (10)

The acceleration ^(T)(a₂x, a₂z) of the center of gravity G2 of the crus11 is determined by the means 35 for calculating the acceleration ofeach portion of a leg. The joint reaction force ^(T)(F₁x, F₁z) acting onthe ankle joint 12 of the distal portion of the crus 11 is approximatelyequal to the estimated value of the floor reaction force determined bythe floor reaction force estimating means 39 on the leg 2 having thecrus 11. To be more specific, in a single stance state, if the leg 2 isin contact with the ground, then the joint reaction force ^(T)(F₁x, F₁z)is the floor reaction force ^(T)(Fx, Fz) determined according to theabove Equation (2). If the leg 2 is a free leg, then ^(T)(F₁x,F₁z)=^(T)(0, 0). In a double stance state, if the leg 2 is the leg atthe rear side relative to the advancing direction of the human being 1,then the joint reaction force ^(T)(F₁x, F₁z) is the floor reaction force^(T)(Frx, Frz) of the above Equation (5), whereas if the leg 2 is at thefront side, then it is the floor reaction force ^(T)(Ffx, Ffz) of theabove Equation (5).

Thus, the joint reaction force ^(T)(F₂x, F₂z) acting on the knee joint10 of each leg 2 is determined according to the above Equation (10) fromthe data of the acceleration ^(T)(a₂x, a₂z) of the center of gravity G2of the crus 11 determined by the means 35 for calculating theacceleration of each portion of a leg, the data of the floor reactionforce (=^(T)(F₁x, F₁z)) determined by the floor reaction forceestimating means 39, the data of the weight m₂ of the crus 11 determinedin advance, and the value of the gravity acceleration g.

Referring to FIG. 8, the moment acting on the ankle joint 12 of thedistal portion of the crus 11 is denoted by M₁, the moment acting on theportion of the knee joint 10 of the crus 11 is denoted by M₂, theinertial moment about the center of gravity G2 of the crus 11 is denotedby I_(G2), and the angular acceleration about the center of gravity G2of the crus 11 is denoted by a₂. In association with FIG. 4 mentionedabove, if the distance between the center of gravity G2 of the crus 11and the center of the knee joint 10 is denoted by t2, and the distancebetween the center of gravity G2 of the crus 11 and the ankle 12 isdenoted by t2′ (=Ld−t2), then the equation of motion related to therotational motion about the center of gravity G2 of the crus 11 will beEquation (11) shown below:

$\begin{matrix}{\begin{matrix}{{I_{G\; 2} \cdot \alpha_{2}} = {M_{1} - M_{2} + {F_{1}{x \cdot t}\;{2^{\prime} \cdot \cos}\;\theta\; d} - {F_{1}{z \cdot t}\;{2^{\prime} \cdot \sin}\;\theta\; d} +}} \\{{F_{2}{x \cdot t}\;{2 \cdot \cos}\;\theta\; d} - {F_{2}{z \cdot t}\;{2 \cdot \sin}\;\theta\; d}}\end{matrix}{{therefore},\begin{matrix}{M_{2} = {M_{1} - {I_{G\; 2} \cdot \alpha_{2}} + {F_{1}{x \cdot t}\;{2^{\prime} \cdot \cos}\;\theta\; d} - {F_{1}{z \cdot t}\;{2^{\prime} \cdot \sin}\;\theta\; d} +}} \\{{{F_{2}{x \cdot t}\;{2 \cdot \cos}\;\theta\; d} - {F_{2}{z \cdot t}\;{2 \cdot \sin}\;\theta\; d}}\;}\end{matrix}}} & (11)\end{matrix}$

where M₁ in Equation (11) denotes the moment obtained in terms of theouter product (vector product) of the floor reaction force acting pointvector determined as described above by the floor reaction force actingpoint estimating means 38 on the leg 2 having the crus 11 related toEquation (11) and the floor reaction force vector determined by thefloor reaction force estimating means 39 on the leg 2. Further, α₂denotes the angular acceleration of the crus 11 determined by the means36 for calculating the angular acceleration of each portion of a leg.Further, θd denotes the inclination angle of the crus 11 determined bythe leg posture calculating means 29. Further, ^(T)(F₁x, F₁z) denotesthe estimated value of a floor reaction force determined by the floorreaction force estimating means 39 as described above. Further,^(T)(F₂x, F₂z) is determined according to the above Equation (10).Further, the inertial moment l_(G2) is determined together with the dataor the like of the weight m₂ and size of the crus 11 and stored in thearithmetic processing unit 16 beforehand.

Accordingly, the moment M₂ acting on the knee joint 10 is determined bythe above Equation (11) from the data of the estimated value of a floorreaction force obtained by the floor reaction force estimating means 39,the data of the estimated value of a floor reaction force acting pointvector obtained by the floor reaction force acting point estimatingmeans 38, the data of the angular acceleration a₂ of the crus 11obtained by the means 36 for calculating the angular acceleration ofeach portion of a leg, the data of the inclination angle θd of the crus11 obtained by the leg posture calculating means 29, the data of thejoint reaction force ^(T)(F₂x, F₂z) determined according to the aboveEquation (10), and the data of the inertial moment I_(G2), the size(Ld), and the position (t2) of the center of gravity G2 of the crus 11determined in advance.

After determining the moment M₂ acting on the portion of the knee joint10 of the crus 11 as described above, the joint moment estimating means40 determines the moment acting on the portion of the hip joint 8 of thethigh 9 by the same processing as the calculation processing therefor.The basic concept of this processing is the same as that of thetechnique for determining the moment M₂ of the knee joint 10, so thatdetailed illustration and explanation will be omitted, an outlinethereof being given below.

First, the joint reaction force ^(T)(F₃x, F₃z) acting on the portion ofthe hip joint 8 of the thigh 9 is determined according to the followingEquation (12) (equation having the same form as that of the aboveEquation (10)) based on the equation of motion related to thetranslational motion of the center of gravity G1 of the thigh 9 (referto FIG. 4).^(T)(F ₃ x,F ₃ z)=^(T)(F ₂ x−m ₁ ·a ₁ x,F ₂ z−m ₁ ·a ₁ z−m ₁ ·g)  (12)

where ^(T)(F₂x, F₂z) denotes a joint reaction force of the knee joint 10determined previously according to the Equation (10). Further, ^(T)(a₁x,a₁z) denotes an acceleration (translational acceleration), in theabsolute coordinate system Cf, of the center of gravity G1 of the thigh9 determined by the means 35 for calculating the acceleration of eachportion of a leg. Further, m₁ denotes the weight of the thigh 9determined in advance, and g denotes a gravitational acceleration.

Subsequently, a moment M₃ acting on the portion of the hip joint 8 ofthe thigh 9 is determined according to Equation (13) given below (anequation of the same form as that of the above Equation (11)) on thebasis of the equation of motion related to a rotational motion about thecenter of gravity G1 of the thigh 9.M ₃ =M ₂ −I _(G1)α₁ +F ₂ x·t1′·cos θc−F ₂ z·t1′·sin θc+F ₃ x·t1·cos θc−F₃ z·t1·sin θc  (13)

M₂ denotes the moment of the knee joint 10 determined according to theabove Equation (11), ^(T)(F₂x, F₂z) denotes a joint reaction force ofthe knee joint 10 determined according to the Equation (10), ^(T)(F₃x,F₃z) denotes a joint reaction force of the hip joint 8 determinedaccording to the Equation (12), I_(G1) denotes an inertial moment aboutthe center of gravity G1 of the thigh 9 determined in advance, α₁denotes an angular acceleration of the thigh 9 determined by the means36 for calculating the angular acceleration of each portion of a leg,and θc denotes an inclination angle of the thigh 9 determined by the legposture calculating means 29. Further, t1 denotes the distance from thecenter of the hip joint 8 to the center of gravity G1 of the thigh 9(refer to FIG. 4), and t1′ denotes the distance from the center of kneejoint 10 to the center of gravity G1 of the thigh 9 (L_(c)−t1 in FIG.4), these being decided on the basis of the position of the center ofgravity G1 and the size (length) of the thigh 9 determined in advance.

The processing explained above is successively executed at each cycletime of the arithmetic processing unit 16 to estimate, in real-time, thefloor reaction force acting on each leg 2 and the moments acting on theknee joint 10 and the hip joint 8 of each leg 2.

Although detailed explanation in the present specification will beomitted, the estimated values of the moments of the knee joint 10 andthe hip joint 8 that have been determined are used for, e.g.,controlling an apparatus that aids the walking of the human being 1 (anapparatus that includes an electric motor or the like capable ofimparting auxiliary torque to the knee joint 10 or the hip joint 8).

Examples of the time-dependent changes in the estimated value of a floorreaction force acting point determined by the processing of thearithmetic processing unit 16 described above are indicated by the solidlines in FIG. 9 and FIG. 10. FIG. 9 and FIG. 10 show, with the solidlines, the time-dependent changes in a component in the x-axis direction(a horizontal component in the advancing direction) and a component inthe z-axis direction (a vertical component) of the estimated value of afloor reaction force acting point of a leg 2 from the moment the leg 2comes in contact with the ground to the moment it leaves the floor whenthe human being 1 is walking on a level ground at a moving speed of, forexample, about 4.5 km/h. In this case, the component in the x-axisdirection shown in FIG. 9 has been converted to the absolute coordinatesystem Cf fixed to the floor A. The component in the z-axis directionshown in FIG. 10 is expressed in terms of a z-axis coordinate value(corresponding to the vertical distance from the center of the hip joint8 to a floor reaction force acting point) in the bodily coordinatesystem Cp. FIG. 9 and FIG. 10 also show, with dashed lines, a componentin the x-axis direction and a component in the z-axis direction of afloor reaction force acting point actually measured using a force plateor the like. As seen in these FIG. 9 and FIG. 10, the estimated valuesof the floor reaction force acting points agree with actually measuredvalues with relatively good accuracy.

Regarding the component in the z-axis direction shown in FIG. 10, thedifference between the estimated value and the actually measured valueexhibits a relatively large increase immediately before the leg 2 leavesthe floor. This is because, in the present embodiment, the verticalposition (the position in the z-axis direction) of the floor reactionforce acting point is determined with a fixed vertical distance betweenthe ankle joint 12 and the floor reaction force acting point (beingequal to the distance Ha between the ankle joint and the ground contactsurface in FIG. 5), so that the error of the vertical position of thefloor reaction force acting point increases in such a state wherein theheel side of the foot 13 floats from the floor A, as in the case ofimmediately before the leg 2 leaves the floor.

Supplementally to FIG. 9, this figure, FIG. 9, also shows the calculatedvalues of the positions of the MP joint 13 a, the bodily center ofgravity G0, and the ankle joint 12 in the x-axis direction (the valuesconverted into the absolute coordinate system Cf). Since the position ofa floor reaction force acting point in the x-axis direction in alevel-ground walking mode is estimated as described above, in a periodin which the bodily center of gravity G0 is located behind the anklejoint 12 (the period until time t1), the position of the floor reactionforce acting point in the x-axis direction agrees with the position ofthe ankle joint 12 in the x-axis direction. In a period wherein thebodily center of gravity G0is located between the ankle joint 12 and theMP joint 13 a in the x-axis direction (the period from time t1 to t2),the position of the floor reaction force acting point in the x-axisdirection agrees with the position of the bodily center of gravity G0 inthe x-axis direction. Further, in a period wherein the bodily center ofgravity G0 is located before the MP joint 13 a (the period after timet2), the position of the floor reaction force acting point in the x-axisdirection agrees with the position of the MP joint 13 a in the x-axisdirection.

FIG. 11 to FIG. 20 show, with solid lines, the time-dependent changes ofthe estimated values of the moments of the knee joint 10 and the hipjoint 8. FIG. 11 and FIG. 12 show the knee joint moment and the hipjoint moment, respectively, determined by the arithmetic processing ofthe arithmetic processing unit 16 when the human being 1 performslevel-ground walking at a moving speed of, for example, about 4.5 km/h.FIG. 13 and FIG. 14 show the knee joint moment and the hip joint moment,respectively, determined when the human being 1 walks down a staircase,and FIG. 15 and FIG. 16 show the knee joint moment and the hip jointmoment, respectively, determined when the human being 1 walks up astaircase. Further, FIG. 17 and FIG. 18 show the knee joint moment andthe hip joint moment, respectively, determined when the human being 1sits onto a chair, and FIG. 19 and FIG. 20 show the knee joint momentand the hip joint moment, respectively, determined when the human being1 rises from the chair. These FIG. 11 through FIG. 20 also indicate,with dashed lines, the moments actually measured using a torque meter orthe like. As seen in these FIG. 11 through FIG. 20, the trend of thechanges in the estimated values of the moment exhibits good agreementwith actually measured values. Thus, it is understood that the estimatedpositions of the floor reaction force acting points determined in thepresent embodiment can be determined with sufficiently proper accuracyin estimating the joint moments of the legs 2.

As explained above, the present embodiment makes it possible to estimatethe position of a floor reaction force acting point when the human being1 is walking on a level ground, a staircase or a slope, or sitting ontoa chair or rising from the chair, by a simple technique without using aplurality of types of correlation data or the like to estimate floorreaction force acting points.

A second embodiment of the present invention will now be explained withreference to aforementioned FIG. 2 to FIG. 8 and FIG. 21. The presentembodiment differs from the first embodiment only partly in constructionand processing; therefore, the constructions or functional parts thatare identical to those of the first embodiment will be assigned the samereference numerals and drawings as those of the first embodiment, andthe explanation thereof will be omitted.

Referring to FIG. 2, according to the present embodiment, in a humanbeing 1, an ankle joint angle sensor 24 outputs a signal correspondingto a bending angle Δθe of an ankle joint 12 is attached to the anklejoint 12 of each leg 2, in addition to the devices explained in thefirst embodiment. As in the knee joint angle sensor 23 or the like, theankle joint angle sensor 24 is composed of a potentiometer, and securedto the ankle joint 12 through a belt or the like, which is not shown.Further, the ankle joint angle sensor 24 is connected to an arithmeticprocessing unit 16 through a signal line, which is not shown, to inputits outputs to the arithmetic processing unit 16.

Here, the bending angle Δθe detected by each ankle joint angle sensor 24denotes the angle formed by the line, which connects the center of theankle joint 12 and the center of an MP joint 13 a of a foot 13 linked tothe ankle joint 12, and the axis of a crus 11.

Referring to FIG. 3, in the arithmetic processing unit 16 in the presentembodiment, an output of the above each ankle joint angle sensor 24 isreceived and supplied to an MP position calculating means 33. Furthersupplied to the MP position calculating means 33 are the positions ofthe ankle joint 12 (the positions in the bodily coordinate system Cp)calculated by an ankle position calculating means 32 in the same manneras that in the first embodiment, and also an inclination angle θd of thecrus 11 calculated by a leg posture calculating means 29.

The construction except for that explained above is identical to theconstruction of the first embodiment.

The present embodiment having the construction described above differsfrom the first embodiment only in the processing of the MP positioncalculating means 33 and the processing of a floor reaction force actingpoint estimating means 38 of the arithmetic processing unit 16. Morespecifically, the present embodiment is adapted to grasp the positionsof the MP joint 13 a more accurately than the first embodiment does soas to achieve higher accuracy of estimating the positions of floorreaction force acting points than in the first embodiment. The followingwill explain in detail the processing of the MP position calculatingmeans 33 and the processing of the floor reaction force acting pointestimating means 38 in the present embodiment.

In the processing of the MP position calculating means 33, the positionof the MP joint 13 a (more specifically, the positions in the x-axisdirection and the z-axis direction in a bodily coordinate system Cp) isdetermined as follows by using detection data or the like of the anklejoint angle sensor 24.

Referring to FIG. 21, a segment S connecting the center of the anklejoint 12 and the center of the MP joint 13 a (hereinafter referred to as“the foot main line S”) is assumed, the angle formed by the foot mainline S with respect to the vertical direction (the z-axis direction)(the inclination angle of the foot main line S) is denoted by θe, andthe length of the foot main line S (the distance between the ankle joint12 and the MP joint 13 a) is denoted by Ls. At this time, a distanceΔxmp in the horizontal direction (the x-axis direction) and a distanceΔzmp in the vertical direction (the z-axis direction) between the anklejoint 12 and the MP joint 13 a, that is, a position ^(T)(Δxmp, Δzmp) ofthe MP joint 13 a relative to the ankle joint 12 is given according tothe following Equation (14):^(T)(Δxmp,Δzmp)=(Ls·sin θe,Ls cos θe)  (14)

In this case, the foot 13 may be regarded as substantially a rigid body,and at this time, Ls takes a constant.

Further, the inclination angle θe of the foot main line S is givenaccording to the following Equation (15), using the bending angle Δθe ofthe ankle joint 12 detected by the ankle joint angle sensor 24 and theinclination angle θd of the crus 11 determined by the leg posturecalculating means 29:θe=θd−(180−Δθe)  (15)

In Equation (15), “degrees” is used as the unit of angles.

In the processing of the MP position calculating means 33, theinclination angle θe of the foot main line S is first determinedaccording to the above Equation (15) from the current value of the dataof the inclination angle θd of the crus 11 of each leg 2 determined bythe leg posture calculating means 29, and the current value of thedetection data of the bending angle Δθe of the ankle joint 12 obtainedfrom the ankle joint angle sensor 24 attached to the leg 2. Then, theposition ^(T)(Δxp, Δzmp) of the MP joint 13 a relative to the anklejoint 12 is determined according to the above Equation (14) from thedetermined inclination angle θe and the length Ls of the foot main lineS actually measured beforehand on the human being 1 and stored andretained in the arithmetic processing unit 16. Furthermore, the positionof the MP joint 13 a in the bodily coordinate system Cp is determined bycalculating the vector sum of the position ^(T)(Δxmp, Δzmp) and theposition of the ankle joint 12 determined by the ankle positioncalculating means 32 (the position in the bodily coordinate system Cp)^(T)(x12, z12).

In the processing of the floor reaction force acting point estimatingmeans 38, the horizontal position (the position in the x-axis direction)of a floor reaction force acting point of each leg 2 in contact with theground is determined by the same technique as that in the firstembodiment. Therefore, the explanation of the processing for estimatingthe horizontal positions of floor reaction force acting points will beomitted.

Meanwhile, in the processing of the floor reaction force acting pointestimating means 38, the technique for estimating the vertical position(the position in the z-axis direction) of the floor reaction forceacting point of each leg 2 in contact with the ground is different fromthat in the first embodiment; the vertical position of a floor reactionforce acting point is decided as follows. First, on each leg 2 incontact with the ground, the distance between the ankle joint 12 of theleg 2 and the ground contact surface (a floor A), that is, the distancebetween the ankle joint and the ground contact surface, is grasped. Inthis case, the method for grasping the distance between an ankle jointand a ground contact surface is decided, depending on whether the bodilycenter of gravity G0is located before or behind the MP joint 13 a in thex-axis direction. If the bodily center of gravity G0is located behindthe MP joint 13 a, then it is generally considered that the bottom ofthe heel of a foot 13 is substantially in contact with the floor A or ispositioned at substantially the same height as the surface of the floorA. In this case, therefore, the aforesaid ankle joint reference heightHa actually measured when the human being 1 is in an upright stationarystate and stored and retained beforehand in the arithmetic processingunit 16 (refer to FIG. 5) is grasped as the distance between the anklejoint and the ground contact surface.

If the bodily center of gravity G0is located before the MP joint 13 a,then the heel of the foot 13 is usually floating above the surface ofthe floor A. In this case, the distance between the ankle joint and theground contact surface is calculated as follows. Referring to theaforesaid FIG. 21, if the heel of the foot 13 is floating above thesurface of the floor A, then the distance between the ankle joint andthe ground contact surface will be the sum of the vertical distance Δzmpbetween the ankle joint 12 and the MP joint 13 a and the distancebetween the MP joint 13 a and the ground contact surface (the surface ofthe floor A). In this case, the distance between the MP joint 13 a andthe ground contact surface is substantially identical to a distance Hbbetween the MP joint 13 a and the surface of the floor A (hereinafterreferred to as “the MP joint reference height Hb”) in a state whereinthe human being 1 is standing in an upright posture with substantiallythe entire sole of the foot 13 in contact with the floor A (in theaforesaid upright stationary state), as shown in FIG. 5. Hence,according to the present embodiment, the MP joint reference height Hb isactually measured together with the ankle joint reference height Habeforehand and stored and retained in the arithmetic processing unit 16.And, if the bodily center of gravity G0is located before the MP joint 13a, then the sum of the vertical distance Δzmp between the ankle joint 12and the MP joint 13 a grasped from the positions of these joints in thebodily coordinate system Cp and the MP joint reference height Hb isdetermined as the distance between the ankle joint and the groundcontact surface.

The MP joint reference height Hb may be actually measured and retainedin a memory for each foot 13, or the actually measured value of only onefoot 13 may be shared for both feet 13 and 13. In correspondence to thefloor reaction force acting point estimating method in accordance withthe present invention, the ankle joint reference height Ha and the MPjoint reference height Hb correspond to a first basic vertical distanceand a second basic vertical distance, respectively.

After the distance between the ankle joint and the ground contactsurface is grasped as described above, the vertical position (theposition in the z-axis direction) of a floor reaction force acting pointis determined as the position vertically apart downward from theposition of the ankle joint 12 by the grasped distance between the anklejoint and the ground contact surface in the same manner as that in thefirst embodiment. In other words, the vertical position (the position inthe bodily coordinate system Cp) of the floor reaction force actingpoint is determined as the value obtained by subtracting the distancebetween the ankle joint and the ground contact surface, which has beengrasped as described above, from the value of the z-axis component ofthe position of the ankle joint 12 (the upward direction being definedas the positive direction of the z-axis).

In the present embodiment also, as in the first embodiment, in order tocalculate a joint moment by a joint moment estimating means 40, theposition in the bodily coordinate system Cp of the floor reaction forceacting point decided as described above (xz-coordinate component) isconverted into a position defined using the position of the ankle joint12 in the bodily coordinate system Cp calculated by the ankle positioncalculating means 32 as its reference.

The processing of the arithmetic processing unit 16 except for the MPposition calculating means 33 and the floor reaction force acting pointestimating means 38 explained above is the same as that in the firstembodiment.

The present embodiment makes it possible to grasp the positions of theMP joint 13 a (the positions in the x-axis direction and the z-axisdirection) with relatively high accuracy, thus allowing the positions,particularly the vertical positions, of floor reaction force actingpoints to be estimated with higher accuracy than that in the firstembodiment. As a result, the joint moments acting on the knee joint 10and the hip joint 8 can be estimated also with higher accuracy than thatin the first embodiment.

The distance between an ankle joint and a ground contact surfacedetermined to estimate the vertical position of a floor reaction forceacting point can be determined by a technique other than the techniquesexplained in the first embodiment and the second embodiment. Forexample, an optical distance measuring sensor, such as an infrareddistance measuring sensor, is attached to an appropriate portion of thecrus 11 of each leg 2 (specifically, the portion apart from the anklejoint 12 toward the knee joint 10 by a predetermined distance in theaxial direction of the crus 11), and the distance in the axial directionof the crus 11 between the portion to which the distance measuringsensor has been attached and a floor surface (the ground contact surfaceof the leg 2) is measured. Then, from the measured distance and theinclination angle θd of the crus 11, the vertical distance between theportion equipped with the distance measuring sensor and the floorsurface (hereinafter referred to as “the distance between the sensor andthe floor surface”) is calculated by geometric computation(trigonometric function computation). Further, from the distance betweenthe portion equipped with the distance measuring sensor and the anklejoint 12 (a fixed value) and the inclination angle θd of the crus 11,the vertical distance between the portion and the ankle joint 12 isdetermined by the trigonometric function computation, and then thedetermined vertical distance is subtracted from the aforesaid distancebetween the sensor and the floor surface so as to determine the distancebetween the ankle joint and the ground contact surface. Thus,determining the distance between the ankle joint and the ground contactsurface makes it possible to accurately estimate the vertical positionof a floor reaction force acting point without using the ankle jointangle sensor 24. In this case, the horizontal position of a floorreaction force acting point may be estimated using the same technique asthat of the first embodiment.

In the embodiments explained above, the examples, in which the presentinvention has been applied to the human being 1, have been explained;however, the present invention can be applied also to a biped walkingrobot as a biped walking mobile body.

INDUSTRIAL APPLICABILITY

As is obvious from the above explanation, the present invention makes itpossible to estimate a joint moment of a leg of a biped walking mobilebody, such as a human being, so that the estimated joint moment can beapplied for controlling the operation of a walking aid apparatus or thelike that aids the walking of a human being. For example, a part of theestimated joint moment may be generated by the walking aid apparatus soas to conduct control for reducing load on the human being.

1. A method of successively estimating the position of a floor reactionforce acting point of each leg of a biped walking mobile body,comprising: a first step for successively grasping the position of thecenter of gravity of the biped walking mobile body, the position of theankle joint of each leg, and the position of the metatarsophalangealjoint of the foot of the leg, respectively, and also successivelygrasping the vertical distance from the ankle joint to a ground contactsurface of each leg in contact with the ground while the biped walkingmobile body is in motion, a first ground contact sensor and a secondground contact sensor being provided on the sole of the foot of each legof the biped walking mobile body, and the first and the second groundcontact sensors outputting ground contact detection signals based onwhether a place directly below an ankle joint of a leg and a placedirectly below a metatarsophalangeal joint of the foot of the leg,respectively, are in contact with the ground; and a second step wherein,for each leg in contact with the ground while the biped walking mobilebody is in motion, the horizontal position of one of the center ofgravity, the ankle joint of the leg, and the metatarsophalangeal jointof the leg, the positions thereof having been determined in the firststep, is successively estimated selectively as the horizontal positionof the floor reaction force acting point of the leg on the basis of atleast the combination of contact or no contact with the ground indicatedby a ground contact detection signal of the first ground contact sensorand contact or no contact with the ground indicated by a ground contactdetection signal of the second ground contact sensor of each leg, andthe vertical position of the floor reaction force acting point of theleg is successively estimated as the position apart vertically downwardfrom the ankle joint by the vertical distance from the ankle joint tothe ground contact surface of the leg determined in the first step. 2.The method of estimating a floor reaction force acting point of a bipedwalking mobile body according to claim 1, wherein, when estimating thehorizontal position of the floor reaction force acting point in thesecond step, on each leg in contact with the ground, if a ground contactdetection signal of the first ground contact sensor of each leg is asignal indicating contact with the ground and a ground contact detectionsignal of the second ground contact sensor of the leg is a signalindicating no contact with the ground, then the horizontal position ofthe ankle joint of the leg is estimated as the horizontal position of afloor reaction force acting point of the leg, or if a ground contactdetection signal of the first ground contact sensor of each leg is asignal indicating no contact with the ground and a ground contactdetection signal of the second ground contact sensor of the leg is asignal indicating contact with the ground, then the horizontal positionof the metatarsophalangeal joint of the leg is estimated as thehorizontal position of the floor reaction force acting point of the leg,or if ground contact detection signals of both the first ground contactsensor and the second ground contact sensor of each leg are signalsindicating contact with the ground and if the position of the center ofgravity is behind the position of the ankle joint of the leg in theadvancing direction of the biped walking mobile body, then thehorizontal position of the ankle joint of the leg is estimated as thehorizontal position of the floor reaction force acting point of the leg,or if ground contact detection signals of both the first ground contactsensor and the second ground contact sensor of each leg are signalsindicating contact with the ground and if the position of the center ofgravity is before the position of the metatarsophalangeal joint of theleg in the advancing direction of the biped walking mobile body, thenthe horizontal position of the metatarsophalangeal joint of the leg isestimated as the horizontal position of the floor reaction force actingpoint of the leg, or if ground contact detection signals of both thefirst ground contact sensor and the second ground contact sensor of eachleg are signals indicating contact with the ground and if the positionof the center of gravity is between the position of the ankle joint andthe position of the metatarsophalangeal joint of the leg in theadvancing direction of the biped walking mobile body, then thehorizontal position of the center of gravity is estimated as thehorizontal position of the floor reaction force acting point of the leg.3. The method of estimating a floor reaction force acting point of abiped walking mobile body according to claim 1, wherein the verticaldistance from the ankle joint to a ground contact surface of each legwhen the biped walking mobile body is in an upright stationary state ismeasured and retained in a memory beforehand, and when grasping thevertical distance from the ankle joint to the ground contact surface ofeach leg in contact with the ground in the first step, the verticaldistance retained in the memory is grasped as the vertical distance fromthe ankle joint to the ground contact surface of each leg in contactwith the ground.
 4. The method of estimating a floor reaction forceacting point of a biped walking mobile body according to claim 1,wherein the vertical distance from the ankle joint to a ground contactsurface of each leg and the vertical distance from themetatarsophalangeal joint to the ground contact surface of the leg whenthe biped walking mobile body is in an upright stationary state aremeasured and retained in a memory beforehand as a first basic verticaldistance and a second basic vertical distance, respectively, and whengrasping the vertical distance from the ankle joint to the groundcontact surface of each leg in contact with the ground in the firststep, if the position of the center of gravity is behind the position ofthe metatarsophalangeal joint of the leg in the advancing direction ofthe biped walking mobile body, then the first basic vertical distance isgrasped as the vertical distance from the ankle joint to the groundcontact surface of the leg, or if the position of the center of gravityis before the position of the metatarsophalangeal joint of the leg inthe advancing direction of the biped walking mobile body, then thevertical distance between the ankle joint and the metatarsophalangealjoint of the leg is determined, and then the value obtained by addingthe second basic vertical distance to the determined vertical distanceis grasped as the vertical distance from the ankle joint to the groundcontact surface of the leg.
 5. A method of estimating a joint moment ofa biped walking mobile body for estimating a moment acting on at leastone joint of each leg of the biped walking mobile body by using anestimated value of the position of a floor reaction force acting pointsuccessively determined by the method of estimating a floor reactionforce acting point of a biped walking mobile body according to claim 1,comprising: a step for successively estimating the floor reaction forceof each leg, which is in contact with the ground, of the biped walkingmobile body by using at least a detection output of an accelerationsensor attached to a body of the biped walking mobile body to detect theacceleration of a predetermined part of the body and a detection outputof a body inclination sensor attached to the body to detect aninclination angle of the body, and a step for successively grasping theinclination angle of each rigid corresponding part of a biped walkingmobile body that corresponds to each rigid body of a rigid link modelrepresenting the biped walking mobile body in the form of a linkassembly of a plurality of rigid bodies, the acceleration of the centerof gravity of the rigid corresponding part, and the angular accelerationof the rigid corresponding part by using at least detection outputs ofthe body inclination sensor and an angle sensor attached to a joint ofeach leg of the biped walking mobile body to detect the bending angle ofthe joint, wherein a moment acting on at least one joint of each leg ofthe biped walking mobile body is estimated on the basis of an inversedynamics model by using an estimated value of the floor reaction force,an estimated value of the position of the floor reaction force actingpoint, an inclination angle of the each rigid corresponding part, theacceleration of the center of gravity of the rigid corresponding partand the angular acceleration of the rigid corresponding part, weight andsize of each rigid corresponding part that have been determined inadvance, the position of the center of gravity of each rigidcorresponding part in the rigid corresponding part that has beendetermined in advance, and the inertial moment of each rigidcorresponding part that has been determined in advance.